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Most recent 20 results returned for keyword: Main Sequence (Search this on MAP)

https://plus.google.com/106136236199326198859 SՆ૯૯ƿע (Super duper tesco cashier) : The Giant Squid in the Flying Bat (Sh 2-129 and Ou4) In this amazing image taken by +Nicolas Kizilian...
The Giant Squid in the Flying Bat (Sh 2-129 and Ou4)

In this amazing image taken by +Nicolas Kizilian using a William Optics Zenithstar 66 refractor with a WO Flattener 6 and a Moravian G2-8300 you can see Ou4 (The Giant Squid Nebula) within Sh 2-129 (The Flying Bat Nebula). Total exposure time was 25 hours, 20 minutes.

The objects are located in the constellation of Cepheus (https://goo.gl/h8tIIA), about 2,300 light-years away from Earth. If the estimates of distance and location for Ou4 are correct, its long axis has a length of about 50 light-years.

Sh 2-129, the Flying Bat Nebula (the red nebula in the image) is an emission nebula. Located within this emission nebula is Ou4, the Giant Squid Nebula (the blue-green nebula in the image).

Research suggests that Ou4 is a bipolar outflow (https://goo.gl/IRvZPO) launched by the triple star system HR8119, consisting of three B-type main-sequence stars (https://goo.gl/sciCuH), about 90,000 years ago. The tips of the two lobes are moving at speeds of 83 kilometers/second and 112 kilometers/second. It is however also possible, that Ou4 is a bipolar planetary nebula (see Hen 2-437 here: https://goo.gl/cgZijr).

More information here:
http://apod.nasa.gov/apod/ap150911.html
http://apod.nasa.gov/apod/ap140718.html

Paper regarding the Ou4 outflow:
http://arxiv.org/abs/1407.4617

What is an emission nebula?

An emission nebula is a cloud of ionized gas (often by ultraviolet radiation from nearby stars) emitting light of various colors (in case of Hydrogen mostly reddish-pink). More information here:
https://en.wikipedia.org/wiki/Emission_nebula
https://en.wikipedia.org/wiki/H_II_region

Image credit: Sh 2-129 and Ou4 +Nicolas Kizilian https://goo.gl/XByRWx Used with permission

If you like this image, you can find Nicolas here on G+ (+Nicolas Kizilian) and on Facebook (https://www.facebook.com/NicolasKizilian) and see more of his work here on his website:
http://www.astropixels.fr

Thank you for your interest in this Astronomy/Astrophysics collection. Maybe add me on Google+ (+Pierre Markuse) and Twitter (https://twitter.com/Pierre_Markuse) or have a look at the Space/Space Technology collection here: https://goo.gl/5KP0wx

#science #astronomy #astrophotograpy #emissionnebula #sh2129 #ou4 #bipolaroutflow #space #bipolarnebula 
https://lh3.googleusercontent.com/-1KUbpdBEw24/V9pnmit_NgI/AAAAAAAA1Ss/p8hDq42BHsgO0AR2Da5mzUlxhQhHzKuDwCL0B/w506-h750/Sh2-129-ou4-Kizilian-1-1920.jpg
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https://plus.google.com/118210557303864143794 Tania From Australia : #Brown #Dwarfs Brown dwarfs are substellar objects that occupy the mass range between the heaviest ...
#Brown #Dwarfs

Brown dwarfs are substellar objects that occupy the mass range between the heaviest gas giants and the lightest stars, of approximately 13 to 75–80 Jupiter masses (MJ).

Below this range are the sub-brown dwarfs, sometimes referred to as rogue planets, and above it are the lightest red dwarfs (M9 V). Brown dwarfs may be fully convective, with no layers or chemical differentiation by depth.

Unlike the stars in the main-sequence, brown dwarfs are not massive enough to sustain nuclear fusion of ordinary hydrogen (1H) to helium in their cores. They are, however, thought to fuse deuterium (2H) and to burn lithium (7Li) if their mass is above a debated[4] threshold of 13 MJ and 65 MJ, respectively.

It is also debated whether brown dwarfs would be better defined by their formation processes rather than by their supposed nuclear fusion reactions.

Stars are categorized by spectral class, with brown dwarfs designated as types M, L, T, and Y. Despite their name, brown dwarfs are of different colors. Many brown dwarfs would likely appear magenta to the human eye, or possibly orange/red.
Brown dwarfs are not very luminous at visible wavelengths.

Read more here: https://en.wikipedia.org/wiki/Brown_dwarf

You can check out my channel for more space info.
https://www.youtube.com/channel/UClTW8hInWWrvVB-tw1DRWFQ

Thank you so much!
nemesis maturity channel
https://lh3.googleusercontent.com/-WficS8kAFe4/V-AVYvzrQRI/AAAAAAAAKq8/ErflrNltTzEnatYJvO1gCudgOPrLeW3ogCJoC/w506-h750/ezgif.com-video-to-gif%2B%252822%2529.gif
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https://plus.google.com/113854508329678785099 Oliviero Giammarroni : The Most Mysterious Star in the Universe In this way astronomer Tabetha (“Tabby”) Boyajian named a ...
The Most Mysterious Star in the Universe

In this way astronomer Tabetha (“Tabby”) Boyajian named a TED talk about a puzzling celestial body that has inspired otherwise sober scientists to brainstorm outlandish hypotheses.

Something massive, with roughly 1,000 times the area of Earth, is blocking the light coming from a distant star known as KIC 8462852, and nobody is quite sure what it is. As astronomer Tabetha Boyajian investigated this perplexing celestial object, a colleague suggested something unusual: "Could it be an alien-built megastructure?"
Such an extraordinary idea would require extraordinary evidence.

► In this TED talk, Boyajian gives us a look at how scientists search for and test hypotheses when faced with the unknown.>>
http://www.ted.com/talks/tabetha_boyajian_the_most_mysterious_star_in_the_universe

KIC 8462852 (eponymously Tabby's Star after the initial study's lead author Tabetha S. Boyajian, or WTF Star, formally for "Where's The Flux?", but also a reference to an expression of disbelief) is an F-type main-sequence star located in the constellation Cygnus approximately 1,480 ly from Earth.

Unusual light fluctuations of the star were discovered by citizen scientists as part of the Planet Hunters project (https://www.planethunters.org/), and in September 2015 astronomers and citizen scientists associated with the project posted a preprint of a paper on arXiv describing the data and possible interpretations.

► Watch the preprint "Planet Hunters X. KIC 8462852 - Where's the Flux?">>
https://arxiv.org/abs/1509.03622

The discovery was made from data collected by the Kepler space telescope, which observes changes in the brightness of distant stars in order to detect exoplanets.
KIC 8462852 is the only known star with such behavior among the 150,000 stars monitored by the Kepler mission.

► Read "Mysterious Happenings Around the Star KIC 846852">>
https://www.cfa.harvard.edu/news/su201620

Several hypotheses have been proposed to explain the star's large irregular changes in brightness as measured by its unusual light curve. The leading hypothesis, based on a lack of observed infrared light, is that of a swarm of cold, dusty comet fragments in a highly eccentric orbit.
Many small masses in "tight formation" orbiting the star have also been proposed. The changes in brightness could be signs of activity associated with intelligent extraterrestrial life building a Dyson swarm.
The SETI Institute's initial radio reconnaissance of KIC 8462852, however, found no evidence of technology-related radio signals from the star.

► Image: What is causing the star KIC 8462852 to behave so strangely? A huge belt of debris around it, or ... something else?
Artist drawing by NASA/JPL-Caltech/T. Pyle (SSC)>>
http://astropix.ipac.caltech.edu/image/spitzer/sig05-027

Further reading and references

► KIC 8462852>>
https://en.wikipedia.org/wiki/KIC_8462852

► Help astronomers observe Tabby’s Star>>
http://earthsky.org/space/kic8462852-tabbys-star-alien-megastructure-dyson-sphere-kickstarter

► The Most Mysterious Star in the Galaxy>>
http://blogs.scientificamerican.com/guest-blog/the-most-mysterious-star-in-the-galaxy/

► Did Astronomers Find Evidence of an Alien Civilization? (Probably Not. But Still Cool.)>>
http://www.slate.com/blogs/bad_astronomy/2015/10/14/weird_star_strange_dips_in_brightness_are_a_bit_baffling.html

#universe, #KIC8462852, #TabbysStar, #PlanetHuntersproject, #research, #Keplermission, #exoplanets, #WTFStar
https://lh3.googleusercontent.com/-Q99gMQqCBVQ/V6s7iT-NV-I/AAAAAAABI3g/DsYVq-G1iWUanV2rE9cEVMbeic97QWoPw/w506-h750/spitzer_sig05-027_1280%2B%25281%2529.jpg
2 days ago - Via Reshared Post - View -
https://plus.google.com/114512552693166475149 Wahyu Yon : Fraser Cain "" Does Our Galaxy Have a Habitable Zone?  ""<>----- Published on Sep 19, 2016 It’s not ...
Fraser Cain
"" Does Our Galaxy Have a Habitable Zone?  ""<>-----
Published on Sep 19, 2016
It’s not just our Solar System that has a habitable zone, it turns out our entire galaxy has regions which would be hostile to the formation of life as we know it.

Support us at: http://www.patreon.com/universetoday
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Team: Fraser Cain -@fcain
Jason Harmer -@jasoncharmer
Chad Weber - weber.chad@gmail.com

Created by: Fraser Cain and Jason Harmer
Edited by: Chad Weber
Music: Left Spine Down - “X-Ray”
https://www.youtube.com/watch?v=4tcoZ...

I’ve got to say, you are one of the luckiest people I’ve ever met.

For starters, you are the descendant of an incomprehensible number of lifeforms who were successful, and survived long enough to find a partner, procreate, and have an offspring. Billions of years, and you are the result of an unbroken chain of success, surviving through global catastrophe after catastrophe.

Nice going.

Not only that, but your lineage happened to be born on a planet, which was in just the right location around just the right kind of star. Not too hot, not too cold, just the right temperature where liquid water, and whatever else was necessary for life to get going.

Again, I like your lucky streak.

In fact, you happened to be born into a Universe that has the right physical constants, like the force of gravity or the binding force of atoms, so that stars, planets and even the chemistry of life could happen at all.

But there’s another lottery you won, and you probably didn’t even know about it. You happened to be born on an unassuming, mostly harmless planet orbiting a G-type main sequence star in the habitable zone of the Milky Way.

Wait a second, even galaxies have habitable zones? Yep, and you’re in it right now.

The Milky Way is a big place, measuring up to 180,000 light years across. It contains 100 to 400 billion stars spread across this enormous volume.

We’re located about 27,000 light years away from the center of the Milky Way, and tens of thousands of light-years away from the outer rim.

The Milky Way has some really uninhabitable zones. Down near the center of the galaxy, the density of stars is much greater. And these stars are blasting out a combined radiation that would make it much more unlikely for life to evolve.

Radiation is bad for life. But it gets worse. There’s a huge cloud of comets around the Sun known as the Oort Cloud. Some of the greatest catastrophes in history happened when these comets were kicked into a collision course with the Earth by a passing star. Closer to the galactic core, these disruptions would happen much more often.

There’s another dangerous place you don’t want to be: the galaxy’s spiral arms. These are regions of increased density in the galaxy, where star formation is much more common. And newly forming stars blast out dangerous radiation.

Fortunately, we’re far away from the spiral arms, and we orbit the center of the Milky Way in a nice circular orbit, which means we don’t cross these spiral arms very often.

We stay nice and far away from the dangerous parts of the Milky Way, however, we’re still close enough to the action that our Solar System gathered the elements we needed for life.

The first stars in the Universe only had hydrogen, helium and a few other trace elements left over from the Big Bang. But when the largest stars detonated as supernovae, they seeded the surrounding regions with heavier elements like oxygen, carbon, even iron and gold.

Our solar nebula was seeded with the heavy elements from many generations of stars, giving us all the raw materials to help set evolution in motion.

If the Solar System was further out, we probably wouldn’t have gotten enough of those heavier elements. So, thanks multiple generations of dead stars.

According to astrobiologists the galactic habitable zone probably starts just outside the galactic bulge - about 13,000 light-years from the center, and ends about halfway out in the disk, 33,000 light-years from the center.

Remember, we’re 27,000 light-years from the center, so just inside that outer edge. Phew.

Of course, not all astronomers believe in this Rare Earth hypothesis. In fact, just as we’re finding life on Earth wherever we find water, they believe that life is more robust and resilient. It could still survive and even thrive with more radiation, and less heavier elements.

Furthermore, we’re learning that solar systems might be able to migrate a significant distance from where they formed. Stars that started closer in where there were plenty of heavier elements might have drifted outward to the safer, calmer galactic suburbs, giving life a better chance at getting a foothold.

As always, we’ll need more data, more research to get an answer to this question.
Watch the video: Does Our Galaxy Have a Habitable Zone?
https://lh3.googleusercontent.com/proxy/gnq7elChLp7-WZqqUR90KpZn5JlWm_h3U5mjdQJYrQTrMbxBcY9NVboZFdMlI-TQ31FRv_7M8dRxf_LCDcGlfI37QBg=w506-h284-n
It’s not just our Solar System that has a habitable zone, it turns out our entire galaxy has regions which would be hostile to the formation of life as we kn...
2 days ago - Via Community - View -
https://plus.google.com/114512552693166475149 Wahyu Yon : "" How Can We Save The Sun?  ""<>----- Dipublikasikan tanggal 23 Sep 2016 Bad news, our Sun is living...
"" How Can We Save The Sun?  ""<>-----
Dipublikasikan tanggal 23 Sep 2016
Bad news, our Sun is living on borrowed time. It’s only got a few billion years left. But there might be a way we can extend its life, and make it last for trillions of years into the future.

Support us at: http://www.patreon.com/universetoday
More stories at: http://www.universetoday.com/
Follow us on Twitter:@universetoday
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Team: Fraser Cain -@fcain
Jason Harmer -@jasoncharmer
Chad Weber - weber.chad@gmail.com

Created by: Fraser Cain and Jason Harmer
Edited by: Chad Weber
Music: Left Spine Down - “X-Ray”
https://www.youtube.com/watch?v=4tcoZ...

Remember the movie Sunshine, where astronomers learn that the Sun is dying? So a plucky team of astronauts take a nuclear bomb to the Sun, and try to jump-start it with a massive explosion.

Yeah, there’s so much wrong in that movie that I don’t know where to start. So I just won’t.

Seriously, a nuclear bomb to cure a dying Sun?

Here’s the thing, the Sun is actually dying. It’s just that it’s going to take about another 5 billion years to run of fuel in its core. And when it does, Cillian Murphy won’t be able to restart it with a big nuke.

But the Sun doesn’t have to die so soon. It’s made of the same hydrogen and helium as the much less massive red dwarf stars. And these stars are expected to last for hundreds of billions and even trillions of years.

Is there anything we can do to save the Sun, or jump-start it when it runs out of fuel in the core?

First, let me explain the problem. The Sun is a main sequence star, and it measures 1.4 million kilometers across. Like ogres and onions, the Sun is made of layers.

The innermost layer is the core. That’s the region where the temperature and pressure is so great that atoms of hydrogen are mashed together so tightly they can fuse into helium. This fusion reaction is exothermic, which means that it gives off more energy than it consumes.

The excess energy is released as gamma radiation, which then makes its way through the star and out into space. The radiation pushes outward, and counteracts the inward force of gravity pulling it together. This balance creates the Sun we know and love.

Outside the core, temperatures and pressures drop to the point that fusion can no longer happen. This next region is known as the radiative zone. It’s plenty hot, and the photons of gamma radiation generated in the core of the Sun need to bounce randomly from atom to atom, maybe for hundreds of thousands of years to finally escape.

But it’s not hot enough for fusion to happen.

Outside the radiative zone is the convective zone. This is where the material in the Sun is finally cool enough that it can move around like a lava lamp. Hot blobs of plasma pick up enormous heat from the radiative zone, float up to the surface of the Sun, release their heat and then sink down again.

The only fuel the Sun can use for fusion is in the core, which accounts for only 0.8% of the Sun’s volume and 34% of its mass. When it uses up that hydrogen in the core, it’ll blow off its outer layers into space and then shrink down into a white dwarf.

The radiative zone acts like a wall, preventing the mixing convective zone from reaching the solar core.

If the Sun was all convective zone, then this wouldn’t be a problem, it would be able to go on mixing its fuel, using up all its hydrogen instead of this smaller fraction. If the Sun was more like a red dwarf, it could last much longer.

In order to save the Sun, to help it last longer than the 5 billion years it has remaining, we would need some way to stir up the Sun with a gigantic mixing spoon. To get that unburned hydrogen from the radiative and convective zones down into the core.

One idea is that you could crash another star into the Sun. This would deliver fresh fuel, and mix up the Sun’s hydrogen a bit. But it would be a one time thing. You’d need to deliver a steady stream of stars to keep mixing it up. And after a while you would accumulate enough mass to create a supernova. That would be bad.

But another option would be to strip material off the Sun and create red dwarfs. Stars with less than 35% the mass of the Sun are fully convective. Which means that they don’t have a radiative zone. They fully mix all their hydrogen fuel into the core, and can last much longer.

Imagine a future civilization tearing the Sun into 3 separate stars, each of which could then last for hundreds of billions of years, putting out only 1.5% the energy of the Sun. Huddle up for warmth.

But if you want to take this to the extreme, tear the Sun into 13 separate red dwarf stars with only 7.5% the mass of the Sun. These will only put out .015% the light of the Sun, but they’ll sip away at their hydrogen for more than 10 trillion years.
Watch the video: How Can We Save The Sun?
https://lh3.googleusercontent.com/proxy/2NZpRq8oTIpRuUQYlGDyzMnQhgQrAnLMOW1ECv3-uM362etqX307Q9hQ_chYMvYq7Wp9RDZE8rTfDa4Lb33d29P0OwY=w506-h284-n
Bad news, our Sun is living on borrowed time. It’s only got a few billion years left. But there might be a way we can extend its life, and make it last for t...
2 days ago - Via Community - View -
https://plus.google.com/114012476478735702428 Linda Marquez : [ad_1] Suppose you have just discovered a new X-­?ray binary Suppose you have just discovered a new ...
[ad_1] Suppose you have just discovered a new X-­?ray binary Suppose you have just discovered a new X-­?ray binary, which contains a B2 main sequence star orbiting an unseen companion. The separation of stars is estimated to be 40 million km, and the…
Suppose you have just discovered a new X-­?ray binary
Suppose you have just discovered a new X-­?ray binary Suppose you have just discovered a new X-­?ray binary, which contains a B2 main sequence star orbitin
2 days ago - Via - View -
https://plus.google.com/114409368061844563858 Swagat Bhowmik : How can we save the sun? Remember the movie Sunshine, where astronomers learn that the Sun is dying?...
How can we save the sun?
Remember the movie Sunshine, where astronomers learn that the Sun is dying? So a plucky team of astronauts take a nuclear bomb to the Sun, and try to jump-start it with a massive explosion. Yeah, there’s so much wrong in that movie that I don’t know where to start. So I just won’t.

Seriously, a nuclear bomb to cure a dying Sun?

Here’s the thing, the Sun is actually dying. It’s just that it’s going to take about another 5 billion years to run of fuel in its core. And when it does, Cillian Murphy won’t be able to restart it with a big nuke.

But the Sun doesn’t have to die so soon. It’s made of the same hydrogen and helium as the much less massive red dwarf stars. And these stars are expected to last for hundreds of billions and even trillions of years.

Is there anything we can do to save the Sun, or jump-start it when it runs out of fuel in the core?

First, let me explain the problem. The Sun is a main sequence star, and it measures 1.4 million kilometers across. Like ogres and onions, the Sun is made of layers.



The interior structure of the Sun. Credit: Wikipedia Commons/kelvinsong

The innermost layer is the core. That’s the region where the temperature and pressure is so great that atoms of hydrogen are mashed together so tightly they can fuse into helium. This fusion reaction is exothermic, which means that it gives off more energy than it consumes.

The excess energy is released as gamma radiation, which then makes its way through the star and out into space. The radiation pushes outward, and counteracts the inward force of gravity pulling it together. This balance creates the Sun we know and love.

Outside the core, temperatures and pressures drop to the point that fusion can no longer happen. This next region is known as the radiative zone. It’s plenty hot, and the photons of gamma radiation generated in the core of the Sun need to bounce randomly from atom to atom, maybe for hundreds of thousands of years to finally escape. But it’s not hot enough for fusion to happen.

Outside the radiative zone is the convective zone. This is where the material in the Sun is finally cool enough that it can move around like a lava lamp. Hot blobs of plasma pick up enormous heat from the radiative zone, float up to the surface of the Sun, release their heat and then sink down again.

The only fuel the Sun can use for fusion is in the core, which accounts for only 0.8% of the Sun’s volume and 34% of its mass. When it uses up that hydrogen in the core, it’ll blow off its outer layers into space and then shrink down into a white dwarf.

The radiative zone acts like a wall, preventing the mixing convective zone from reaching the solar core.

If the Sun was all convective zone, then this wouldn’t be a problem, it would be able to go on mixing its fuel, using up all its hydrogen instead of this smaller fraction. If the Sun was more like a red dwarf, it could last much longer.


Red dwarf stars burn for much longer than our Sun. Credit: NASA, ESA, and D. Aguilar (Harvard-Smithsonian Center for Astrophysics)

In order to save the Sun, to help it last longer than the 5 billion years it has remaining, we would need some way to stir up the Sun with a gigantic mixing spoon. To get that unburned hydrogen from the radiative and convective zones down into the core.

One idea is that you could crash another star into the Sun. This would deliver fresh fuel, and mix up the Sun’s hydrogen a bit. But it would be a one time thing. You’d need to deliver a steady stream of stars to keep mixing it up. And after a while you would accumulate enough mass to create a supernova. That would be bad.

But another option would be to strip material off the Sun and create red dwarfs. Stars with less than 35% the mass of the Sun are fully convective. Which means that they don’t have a radiative zone. They fully mix all their hydrogen fuel into the core, and can last much longer.

Imagine a future civilization tearing the Sun into 3 separate stars, each of which could then last for hundreds of billions of years, putting out only 1.5% the energy of the Sun. Huddle up for warmth.

But if you want to take this to the extreme, tear the Sun into 13 separate red dwarf stars with only 7.5% the mass of the Sun. These will only put out .015% the light of the Sun, but they’ll sip away at their hydrogen for more than 10 trillion years.

Stick the Earth in the middle and you’d have some very odd sunrises and sunsets, not to mention orbital dynamics. Created with Universe Sandbox ²

But how can you get that hydrogen off the Sun? Lasers, of course. Using a concept known as stellar lifting, you could direct a powerful solar powered laser at a spot on the Sun’s surface. This would heat up the region, and generate a powerful solar wind. The Sun would be blasting its own material into space. Then you could use magnetic fields or gravity to direct the outflows and collect them into other stars. It boggles our imagination, but it would be a routine task for Type III Civilization engineers on star dismantling duty.

So don’t panic that our Sun only has a few billion years of life left. We’ve got options. Mind bendingly complicated, solar system dismantling options. But still… options.


3 days ago - Via Google+ - View -
https://plus.google.com/104880342407749621862 Samantha Pearl : Chemically peculiar star HR8844 could be a hybrid object Astronomers from the Paris Observatory in ...
Chemically peculiar star HR8844 could be a hybrid object

Astronomers from the Paris Observatory in Meudon, France and the Notre Dame University – Louaize in Zouk Mosbeh, Lebanon, report that an A-type main-sequence star HR8844, could be a hybrid object between two classes of chemically peculiar stars. The discovery was detailed in a paper published Sept. 16 on arXiv.org.

Previous studies described HR8844 as a slowly rotating, fairly bright (V=5.89), superficially normal A0V star. However, the latest research conducted by Richard Monier of the Paris Observatory and his colleagues sheds new light on the real nature of this star.

http://phys.org/news/2016-09-chemically-peculiar-star-hr8844-hybrid.html
https://lh3.googleusercontent.com/-NO-K9mJqW1c/V-MKJF2qMFI/AAAAAAABwAM/jOPrS_Aj9jI_EV83o_5sfvCF1lPhbg_hwCJoC/w506-h750/chemicallype.jpg
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https://plus.google.com/108901876667002638432 Roland Taylor (RolandiXor) : http://mission-illumination.wikia.com/wiki/Quest_(star) Pronounced "Kest", Quest is a tiny but very...
http://mission-illumination.wikia.com/wiki/Quest_(star)

Pronounced "Kest", Quest is a tiny but very hot main sequence star. It's blue, even though it's only 0.75 times the mass of our sun! (Yes, this is sci-fi, but I will always have a reasonable (or reasonable -ish) explanation for seemingly violating or bending the laws of physics and plain old common sense.
8 days ago - Via Google+ - View -
https://plus.google.com/102191925035426200251 Helena Dias : There are plenty of ways Earth could go. It could smash into another planet, be swallowed by a black...
There are plenty of ways Earth could go. It could smash into another planet, be swallowed by a black hole, or get pummeled to death by asteroids. There's really no way to tell which doomsday scenario will be the cause of our planet's demise.

If it is the Sun...

The sun survives by burning hydrogen atoms into helium atoms in its core. In fact, it burns through 600 million tons of hydrogen every second.

"Once hydrogen has stopped burning in the core of the sun, the star has formally left the main sequence and can be considered a red giant," Scudder said. "It will then spend about a billion years expanding and burning helium in its core, with a shell around it where hydrogen is still able to fuse into helium."
...
With each passing day this core, known as a white dwarf, will cool and fade hopelessly out of existence, as if it didn't once host the most lively planet ever discovered in the sweeping canvas of the universe.
The sun will destroy Earth a lot sooner than you might think
There are plenty of ways Earth could go. It...
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https://plus.google.com/114872669588736831759 Kristian Jerslev : Kristian Jerslev, MSc A couple of months ago I wrote that I had handed in my master thesis (https:/...
Kristian Jerslev, MSc

A couple of months ago I wrote that I had handed in my master thesis (https://goo.gl/n8roYw). June the 29th I defended my thesis, and by passing the exam I finished my last exam in my master's degree programme.

The date June 29th 2016 became the day that my childhood dream of becoming an astronomer finally came true. My childhood interest in astronomy is mostly due to my grandfather, who unfortunately passed away about 10 years ago and never lived to see me finish my degree, but I know he would be very proud of my accomplishments.

Since obtaining my degree I have joined the teaching staff at VUC Aarhus (adjunkt in danish), where I have taught part-time for the last couple of years while finishing my degree.

It took until today for me to receive my diploma, so it is in light of this that I waited till today to post this.

The title of my thesis was Helium variations in the galactic globular cluster 47 Tucanae, and my abstract was:

This thesis presents a broadband photometric study of the multiple stellar populations found in the galactic globular cluster 47 Tucanae. We use photometry from the Hubble Space Telescope ACS/WFC in the F606W and F814W filters provided by Milone et al. (2012c) to construct the vertical colour-magnitude diagram. In the vertical colourmagnitude diagram the colour coordinate of a star is transformed to show the orthogonal separation from the sequence ridgeline. The two large population groups of 47 Tucanae are found to be separated on the main sequence as well as the red giant branch, and we relate the separation using isochrone models to a difference in mean He abundance as well as a difference in the abundance of C, N and O. For stars on the main sequence we find a negligible photometric effect from the presence of molecules consisting of C, N and O, so the measured separation between the two population ridgelines is related to a difference in mean He abundance of <∆Y> = 0.011 ± 0.009 in agreement with previous studies. The separation on the red giant branch can not be solely explained by a difference in mean He content, so we suggest the presence of molecules consisting of C, N and O in order to explain the measured separation as well as a difference in the distribution of said molecules in order to explain the measured ridgeline separation. The broadening of each population’s sequence can be explained by the random photometric errors (on the main sequence) and a star-to-star variation in the distribution of C, N and O (on the red giant branch). A difference in luminosity between the location of the red giant branch bump for the two populations is measured and is related to a difference in mean He content of <∆Y> = 0.007 ± 0.005. The range of magnitudes covered by the bump is related to evolution as well as differences in abundances, but the present data is not sufficient enough to disentangle the two effects. The measured difference in mean He abundances fit into the range of He differences that have already been measured for globular clusters throughout the literature.
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https://plus.google.com/115092248484468092248 Vicki Hults : Astronomers observe star reborn in a flash | Hubble Stingray Nebula and Star SAO 244567 | Distance: ...
Astronomers observe star reborn in a flash | Hubble
Stingray Nebula and Star SAO 244567 | Distance: 2700 light years
An international team of astronomers using Hubble have been able to study stellar evolution in real time. Over a period of 30 years dramatic increases in the temperature of the star SAO 244567 have been observed. Now the star is cooling again, having been reborn into an earlier phase of stellar evolution. This makes it the first reborn star to have been observed during both the heating and cooling stages of rebirth.

Even though the Universe is constantly changing, most processes are too slow to be observed within a human lifespan. But now an international team of astronomers have observed an exception to this rule. “SAO 244567 is one of the rare examples of a star that allows us to witness stellar evolution in real time”, explains Nicole Reindl from the University of Leicester, UK, lead author of the study. “Over only twenty years the star has doubled its temperature and it was possible to watch the star ionizing its previously ejected envelope, which is now known as the Stingray Nebula.”

SAO 244567, 2700 light-years from Earth, is the central star of the Stingray Nebula and has been visibly evolving between observations made over the last 45 years. Between 1971 and 2002 the surface temperature of the star skyrocketed by almost 40,000 degrees Celsius. Now new observations made with the Cosmic Origins Spectrograph (COS) on the NASA/ESA Hubble Space Telescope have revealed that SAO 244567 has started to cool and expand.

This is unusual, though not unheard-of [1], and the rapid heating could easily be explained if one assumed that SAO 244567 had an initial mass of 3 to 4 times the mass of the Sun. However, the data show that SAO 244567 must have had an original mass similar to that of our Sun. Such low-mass stars usually evolve on much longer timescales, so the rapid heating has been a mystery for decades.

Back in 2014 Reindl and her team proposed a theory that resolved the issue of both SAO 244567’s rapid increase in temperature as well as the low mass of the star. They suggested that the heating was due to what is known as a helium-shell flash event: a brief ignition of helium outside the stellar core [2].

This theory has very clear implications for SAO 244567’s future: if it has indeed experienced such a flash, then this would force the central star to begin to expand and cool again — it would return back to the previous phase of its evolution. This is exactly what the new observations confirmed. As Reindl explains: “The release of nuclear energy by the flash forces the already very compact star to expand back to giant dimensions — the born-again scenario.”

It is not the only example of such a star, but it is the first time ever that a star has been observed during both the heating and cooling stages of such a transformation.

Yet no current stellar evolutionary models can fully explain SAO 244567’s behaviour. As Reindl elaborates: “We need refined calculations to explain some still mysterious details in the behaviour of SAO 244567. These could not only help us to better understand the star itself but could also provide a deeper insight in the evolution of central stars of planetary nebulae.”

Until astronomers develop more refined models for the life cycles of stars, aspects of SAO 244567’s evolution will remain a mystery.

Notes
[1] The other star thought to have experienced the same type of helium flash event (see
[2]) is FG Sagittae, located in the constellation Sagitta, making SAO 244567 the second of its kind. However, other objects undergoing similar “born-again” scenarios are known, including Sakurai’s Object, located in Sagittarius.

[2] Helium flash events, also known as late thermal pulses, occur late in the evolution of about 25% of low- to medium-mass stars. After evolving off the main sequence, these stars enter the red giant phase, where the star expands dramatically. Various changes occur in the star’s chemical and physical composition during this phase, until it has burnt most of the helium available in its core, which is by then composed of carbon and oxygen. Helium fusion continues in a thin shell around the core, but then turns off as the helium becomes depleted. This allows hydrogen fusion to start in a layer above the helium layer. After enough additional helium accumulates, helium fusion is reignited, leading to a thermal pulse which eventually causes the star to expand, cool and brighten temporarily.

More information
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

The results will be presented in the paper “Breaking news from the HST: The central star of the Stingray Nebula is now returning towards the AGB”, published in the Monthly Notices of the Royal Astronomical Society (MNRAS).

The international team of astronomers in this study consists of Nicole Reindl (University of Leicester, UK; Eberhard Karls University, Germany), T. Rauch (Eberhard Karls University, Germany), M. M. Miller Bertolami (UNLP-CONICET, Argentina), H. Todt (University of Potsdam, Germany), K. Werner (Eberhard Karls University, Germany)

Credit: NASA, ESA/Hubble
Release Date: September 13, 016

+Hubble Space Telescope 
+European Space Agency, ESA 
+NASA Goddard 
+Space Telescope Science Institute 

#NASA #Hubble #Astronomy #Space #Science #Star #SAO244567 #Nebula #Stingray #Ara #Cosmos #Universe #ESA #STScI
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https://plus.google.com/102191925035426200251 Helena Dias : New research reveals that a B-type main-sequence star designated HD 30963 has unusual metal overabundances...
New research reveals that a B-type main-sequence star designated HD 30963 has unusual metal overabundances.

"We show that this star, hitherto classified as a B9 III superficially normal star, is actually a new chemically peculiar star of the HgMn type. Spectrum synthesis reveals large overabundances of Mn, Sr, Y, Zr , Pt a nd Hg and pronounced underabundances of He and Ni which are characteristic of HgMn stars. We therefore propose that this interesting object be reclassified as a B9 HgMn star," the scientists wrote in the paper.
HgMn stars are a subclass of chemically peculiar stars—main-sequence A and B stars with unusually strong or weak lines for certain elements.
Besides their chemical composition, they experience very slow rotation with an average velocity of 29 km/s, which leads to extremely sharp-lined spectra. At present, more than 150 HgMn stars are known, and many of them were found in young associations.
Chemically peculiar stars like HD 30963 have magnetic fields, and are therefore great natural atomic and magnetic laboratories for scientists. They are perceived as the best objects for learning about magnetic field models, which could be applied to other classes of stars.
Although HD 30963 was recently investigated by the team, which resulted in its reclassification, very little is yet known about this object. The researchers assume that it has a radius ranging from three to four solar radii and the upper limit of its rotational period is estimated to be 4.12 days.
HD 30963 is a chemically peculiar star, study finds
(Phys.org)—New research conducted by a team of astronomers from the Paris Observatory in Meudon, France and the Notre Dame University – Louaize in Zouk Mosbeh, Lebanon, reveals that a B-type main-sequence star designated HD 30963 has unusual metal overabundances. The findings were presented in a paper published Sept. 12 on the arXiv pre-print paper.
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https://plus.google.com/113909043605186374111 Vladimir Pecha : The brightest star visible from any part of Earth is Sirius in the constellation Canis Major the Greater...
The brightest star visible from any part of Earth is Sirius in the constellation Canis Major the Greater Dog. Sirius is sometimes called the Dog Star.

At 8.6 light-years distance, Sirius is one of the nearest stars to us after the sun. (A light year is nearly 6 trillion miles!) In fact it is the nearest star easily visible to the unaided eye from most of the northern hemisphere. Classified by astronomers as an “A” type star, it is much hotter than our sun, with about surface about 17,000 degrees F (the sun is about 10,000 degrees F). With slightly more than twice the mass of the sun and just less than twice its diameter, Sirius still puts out 26 times as much energy. It is considered a normal (main sequence) star, meaning that it produces most of its energy by converting hydrogen into helium through nuclear fusion.
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https://plus.google.com/113909043605186374111 Vladimir Pecha : HD 30963 is a chemically peculiar star, study finds New research conducted by a team of astronomers...
HD 30963 is a chemically peculiar star, study finds

New research conducted by a team of astronomers from the Paris Observatory in Meudon, France and the Notre Dame University – Louaize in Zouk Mosbeh, Lebanon, reveals that a B-type main-sequence star designated HD 30963 has unusual metal overabundances. The findings were presented in a paper published Sept. 12 on the arXiv pre-print paper.

HD 30963 was classified by previous studies as a B9 III superficially normal star; however, the new research showing abnormal metal abundances, including overabundances of mercury (Hg) and manganese (Mn), indicates that the star should be reclassified as a B9 HgMn star.

The team, led by Richard Monier of the Paris Observatory, observed HD 30963 on five consecutive days in late 2015 using the SOPHIE high-resolution echelle spectrograph installed on the 1.93m reflector telescope at the Haute-Provence Observatory in southeastern France. These observations were part of a broader project aiming to reclassify late B stars in the northern hemisphere.

According to the study, analysis of the data provided by SOPHIE shows that HD 30963 has very high abundances of Hg and Mn, as well as platinum (Pt), yttrium (Y) and zirconium (Zr), larger than 50 times the solar values. The overabundance of Hg is extremely high reaching value of about 150,000 times the solar abundance.

http://phys.org/news/2016-09-hd-chemically-peculiar-star.html
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[1506.05993] Lithium evolution in metal-poor stars: from Pre-Main Sequence to the
Spite plateau

Abstract: Lithium abundance derived in metal-poor main sequence stars is about three times lower than the value of primordial Li predicted by the standard Big Bang nucleosynthesis when the baryon density is taken from the CMB or the deuterium measurements. This disagreement is generally referred ...
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https://plus.google.com/101256595456517878669 Wayne Moulden : UMM look at this - The great escape - III. Placing post-main-sequence evolution of planetary and ...
UMM look at this -  



The great escape - III. Placing post-main-sequence evolution of planetary and binary systems in a Galactic context
Authors:


Veras, Dimitri; Evans, N. Wyn; Wyatt, Mark C.; Tout, Christopher A.
Affiliation:


AA(Department of Physics, University of Warwick, Coventry CV4 7AL, UK; Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK; d.veras@warwick.ac.uk), AB(Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK), AC(Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK), AD(Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK)
Publication:


Monthly Notices of the Royal Astronomical Society, Volume 437, Issue 2, p.1127-1140 (MNRAS Homepage)
Publication Date:


01/2014
Origin:


OUP
Astronomy Keywords:


Oort Cloud, planets and satellites: dynamical evolution and stability, planet, star interactions, stars: AGB and post-AGB, stars: evolution, Galaxy: kinematics and dynamics
Abstract Copyright:


2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
DOI:


10.1093/mnras/stt1905
Bibliographic Code:


2014MNRAS.437.1127V
Abstract
Our improving understanding of the life cycle of planetary systems prompts investigations of the role of the Galenvironment before, during and after asymptotic giant branch (AGB) stellar evolution. Here, we investigate the interplay between stellar mass-loss, Galactic tidal perturbations and stellar flybys for evolving stars which host one planet, smaller body or stellar binary companion and reside in the Milky Way's bulge or disc. We find that the potential evolutionary pathways from a main sequence (MS) to a white dwarf (WD) planetary system are a strong function of Galactocentric distance only with respect to the prevalence of stellar flybys. Planetary ejection and collision with the parent star should be more common towards the bulge. At a given location anywhere in the Galaxy, if the mass-loss is adiabatic, then the secondary is likely to avoid close flybys during AGB evolution, and cannot eventually escape the resulting WD because of Galactic tides alone. Partly because AGB mass-loss will shrink a planetary system's Hill ellipsoid axes by about 20 to 40 per cent, Oort clouds orbiting WDs are likely to be more depleted and dynamically excited than on the MS.
http://adsabs.harvard.edu/abs/2014MNRAS.437.1127V
The great escape - III. Placing post-main-sequence evolution of planetary and bi
Title: The great escape - III. Placing post-main-sequence evolution of planetary and binary systems in a Galactic context. Authors: Veras, Dimitri; Evans, N. Wyn; Wyatt, Mark C.; Tout, Christopher A. Affiliation: AA(Department of Physics, University of Warwick, Coventry CV4 7AL, UK; Institute of ...
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https://plus.google.com/115349651784228374081 upma hans : Fading Star Two thousand light years from Earth is a star known as Epsilon Aurigae. It’s a third magnitude...
Fading Star

Two thousand light years from Earth is a star known as Epsilon Aurigae. It’s a third magnitude star most of the time, but about every 27 years it dims to about half its brightness for nearly two years. The cause of the dimming is a bit of a mystery.

It’s long been thought that the dimming is the result of Epsilon Aurigae being a binary system. With a companion star in a large orbit, it could pass in front of the primary star, making it appear to dim. The star is indeed a binary star (if not a multiple star) but the details of the dimming mechanism have been difficult to pin down.

Historically there have been two main ideas. The first is that Epsilon Aurigae is yellow supergiant about 15 times the mass of the Sun, with a companion of similar mass obscured somewhat by dust. This idea is supported by the fact that the spectrum of Epsilon Aurigae has many of the signatures common to yellow supergiants. However the companion star has a spectral signature more similar to a B-type main sequence star.

The other idea is that Epsilon Aurigae is much smaller, with a mass of 2 to 4 solar masses. This would make it smaller than the B-type companion with a mass of about 6 solar masses. In order for the companion to be much dimmer than Epsilon Aurigae, it would have to be surrounded by a thick disk of dust, and that disk would have to be aligned edge on when seen from Earth. It would be odd for a main sequence star to have a thick dusty disk, since they are more commonly seen around young stars that are still forming.

When the most recent dimming occurred in 2009 – 20011, both amateur astronomy groups and the Spitzer infrared telescope made observations of the transit. It now seems that both models were at least partly right. The model that now seems to best fit the data assumes Epsilon Aurigae is only about 10 solar masses, but it moving toward the end of its life. This means it is much brighter than a main sequence star of similar mass. The B-type companion is therefore much dimmer by comparison. With smaller masses, the two stars would be close enough that the companion would capture gas and dust pushed away from Epsilon Aurigae, thus explaining the companion’s dusty disk.

Fading Star - One Universe at a Time
Epsilon Aurigae dims every 27 years. It's still a bit of a mystery why.
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