The stars and dust of spiral galaxy NGC 891 seen by Hubble edge-on
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Like the blade of a magical weapon from a fantasy tale, the northern edge of spiral galaxy NGC 891 is captured by the Hubble Space Telescope, glowing with the light of billions of stars and interwoven with dark clouds of dust and cold gas.
In reality this cosmic blade is enormous. About the same size as our galaxy, NGC 891 is approximately 100,000 light-years in diameter, making the section visible here around 40,000 light-years in length.
Unlike the Milky Way, however, NGC 891 is unbarred and also exhibits many more filaments of dark gas and dust. Astronomers suggest that these are the result of star formation and supernovae, both of which can expel vast amounts of interstellar material far out into space.
The few bright stars in the foreground are located in our own galaxy.
NGC 891 is located in the constellation Andromeda and lies about 30 million light-years away… that means the light captured by Hubble’s Advanced Camera for Surveys to create the image above began its journey 35 million years after the asteroid impact that led to the extinction of the dinosaurs, and about 26 million years before our ancient African ancestors began walking upright. That may sound like a long trip but, as Douglas Adams so eloquently said, “that’s just peanuts to space!”
Artist's impression of a Y-dwarf, the coldest known type of brown dwarf star. (NASA/JPL-Caltech)
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Sometimes called failed stars, brown dwarfs straddle the line between star and planet. Too massive to be “just” a planet, but lacking enough material to start fusion and become a full-fledged star, brown dwarfs are sort of the middle child of cosmic objects. Only first detected in the 1990s, their origins have been a mystery for astronomers. But a researchers from Canada and Austria now think they have an answer for the question: where do brown dwarfs come from?
If there’s enough mass in a cloud of cosmic material to start falling in upon itself, gradually spinning and collapsing under its own gravity to compress and form a star, why are there brown dwarfs? They’re not merely oversized planets — they aren’t in orbit around a star. They’re not stars that “cooled off” — those are white dwarfs (and are something else entirely.) The material that makes up a brown dwarf probably shouldn’t have even had enough mass and angular momentum to start the whole process off to begin with, yet they’re out there… and, as astronomers are finding out now that they know how to look for them, there’s quite a lot.
So how did they form?
According to research by Shantanu Basu of the University of Western Ontario and Eduard I. Vorobyov from the University of Vienna in Austria and Russia’s Southern Federal University, brown dwarfs may have been flung out of other protostellar disks as they were forming, taking clumps of material with them to complete their development.
Basu and Vorobyov modeled the dynamics of protostellar disks, the clouds of gas and dust that form “real” stars. (Our own solar system formed from one such disk nearly five billion years ago.) What they found was that given enough angular momentum — that is, spin — the disk could easily eject larger clumps of material while still having enough left over to eventually form a star.
Model of how a clump of low-mass material gets ejected from a disk (S. Basu/E. Vorobyev)
The ejected clumps would then continue condensing into a massive object, but never quite enough to begin hydrogen fusion. Rather than stars, they become brown dwarfs — still radiating heat but nothing like a true star. (And they’re not really brown, by the way… they’re probably more of a dull red.)
In fact a single protostellar disk could eject more than one clump during its development, Basu and Vorobyov found, leading to the creation of multiple brown dwarfs.
If this scenario is indeed the way brown dwarfs form, it stands to reason that the Universe may be full of them. Since they are not very luminous and difficult to detect at long distances, the researchers suggest that brown dwarfs may be part of the answer to the dark matter mystery.
“There could be significant mass in the universe that is locked up in brown dwarfs and contribute at least part of the budget for the universe’s missing dark matter,” Basu said. “And the common idea that the first stars in the early universe were only of very high mass may also need revision.”
Based on this hypothesis, with the potential number of brown dwarfs that could be in our galaxy alone we may find that these “failed stars” are actually quite successful after all.
The team’s research paper was accepted on March 1 into The Astrophysical Journal.
Read more on the University of Western Ontario’s news release here.
An ESO telescope captures a group of hot young stars that would outshine any Hollywood party!
At the upper left of this image is the star cluster NGC 6604, a grouping of hot young stars within a larger collection located in the sky near the much more famous Eagle Nebula (of “Pillars of Creation” fame.) The young stars, which burn bright and blue, are helping make a new generation of stars with their strong stellar winds, which condense nearby gas and dust into even more star-forming regions.
Eventually the new stars will replace the ones seen here, which, although big and bright, will quickly burn through their stellar fuel and fade. Such is the life cycle of massive stars — live fast and die young.
This image was acquired by the MPG/ESO 2.2-meter telescope at the European Southern Observatory’s La Silla Observatory in Chile. NGC 6604 is about 5,500 light-years from Earth, located in the constellation Serpens. Read more on the ESO news release here.
Painstakingly assembled from over 150,000 digital photos taken over the course of eight months, this stunning time-lapse video of aurora-filled Arctic skies is the latest creation by photo/video artist Ole C. Salomonsen. Take a moment, turn up the sound, sit back and enjoy the show!
This is Ole’s second video project. The footage was shot on location in parts of Norway, Finland and Sweden from September 2011 to April 2012, and shows the glorious effects that the Sun’s increasing activity has had on our planet’s upper atmosphere.
The video is a merge of two parts; the first part contains some more wild and aggressive auroras, as well as a few Milky Way sequences, hence either auroras are moving fast because they are or they are fast due to motion of the Milky Way / stars. Still, some of the straight-up shots are very close to real-time speed — although auroras mostly are slower, she can also be FAST!
The second part has some more slow and majestic auroras, where I have focused more on composition and foreground. The music should give you a clear indication of where you are.
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The music was provided by Norwegian composer Kai-Anders Ryan.
Ole’s “hectic” aurora season is coming to a close now that the Sun is rising above the horizon in the Arctic Circle, and he figured that it was a good time to release the video. It will also be available on 4K Digital Cinema on request.
“Hope you like the video, and that you by watching it are able to understand my fascination and awe for this beautiful celestial phenomenon,” says Ole.
New Hubble image of Messier 9 cluster resolves individual stars (NASA/ESA)
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First discovered by Charles Messier in 1764, the globular cluster Messier 9 is a vast swarm of ancient stars located 25,000 light-years away, close to the center of the galaxy. Too distant to be seen with the naked eye, the cluster’s innermost stars have never been individually resolved… until now.
This image from the Hubble Space Telescope is the most detailed view yet into Messier 9, capturing details of over 250,000 stars within it. Stars’ shape, size and color can be determined — giving astronomers more clues as to what the cluster’s stars are made of. (Download a large 10 mb JPEG file here.)
Hot blue stars as well as cooler red stars can be seen in Messier 9, along with more Sun-like yellow stars.
Unlike our Sun, however, Messier 9’s stars are nearly ten billion years old — twice the Sun’s age — and are made up of much less heavy elements.
Since heavy elements (such as carbon, oxygen and iron) are formed inside the cores of stars and dispersed into the galaxy when the stars eventually go supernova, stars that formed early on were birthed from clouds of material that weren’t yet rich in such elements.
Zoom into the Messier 9 cluster with a video from NASA and the European Space Agency below:
The Hubble Space Telescope is a project of international cooperation between ESA and NASA. See more at www.spacetelescope.org.
Image credit: NASA & ESA. Video: NASA, ESA, Digitized Sky Survey 2, N. Risinger (skysurvey.org)
Mosaic of infrared survey images from ESO's VISTA reveal over 200,000 distant galaxies. (ESO/UltraVISTA team. Acknowledgement: TERAPIX/CNRS/INSU/CASU.)
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See all those tiny points of light in this image? Most of them aren’t stars; they’re entire galaxies, seen by the European Southern Observatory’s VISTA survey telescope located at the Paranal Observatory in Chile.
This is a combination of over 6000 images taken with a total exposure time of 55 hours, and is the widest deep view of the sky ever taken in infrared light.
The galaxies in this VISTA image are only visible in infrared light because they are very far away. The ever-increasing expansion rate of the Universe shifts the light coming from the most distant objects (like early galaxies) out of visible wavelengths and into the infrared spectrum.
ESO’s VISTA (Visual and Infrared Survey Telescope for Astronomy) telescope is the world’s largest and most powerful infrared observatory, and has the ability to peer deep into the Universe to reveal these incredibly distant, incredibly ancient structures.
By studying such faraway objects astronomers can better understand how the structures of galaxies and galactic clusters evolved throughout time.
The region seen in this deep view is an otherwise “unremarkable” and apparently empty section of sky located in the constellation Sextans.
This video is a compilation of different time-lapses taken from the ISS over the past several months, edited by Alex Rivest and shared on Vimeo. It shows just how incredible the stars can appear from the night side of our planet… and 240 miles up!
In a 2008 interview by TIME magazine, astrophysicist Neil deGrasse Tyson was asked what he thought the “most astounding fact” about the Universe was. Never at a loss for words, the famed scientist gave his equally astounding answer. His response is in the video above, set to images and music by Max Schlickenmeyer.
It’s the best three minutes and thirty-three seconds you’ll spend all day.
Comparison of the habitable zone around the Sun in our solar system and around the star Gliese 581. Credit: ESO
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Habitable zones are the regions around stars, including our own Sun, where conditions are the most favourable for the development of life on any rocky planets that happen to orbit within them. Generally, they are regions where temperatures allow for liquid water to exist on the surface of these planets and are ideal for “life as we know it.” Specific conditions, due to the kind of atmosphere, geological conditions, etc. must also be taken into consideration, on a case-by-case basis.
Now, by examining trace elements in the host stars, researchers have found clues as to how the habitable zones evolve, and how those elements also influence them. To determine what elements are in a star, scientists study the wavelengths of its light. These trace elements are heavier than the hydrogen and helium gases which the star is primarily composed of. Variations in the composition of these stars are now thought to affect the habitable zones around them.
The study was led by Patrick Young, a theoretical astrophysicist and astrobiologist at Arizona State University. Young and his team presented their findings on January 11, 2012 at the annual meeting of the American Astronomical Society in Austin, Texas. He and his colleagues have examined more than a hundred dwarf stars so far.
An abundance of these elements can affect how opaque a star’s plasma is. Calcium, sodium, magnesium, aluminum and silicon have been found to also have small but significant effects on a star’s evolution – higher levels tended to result in cooler, redder stars. As Young explains, “The persistence of stars as stable objects relies on the heating of plasma in the star by nuclear fusion to produce pressure that counteracts the inward force of gravity. A higher opacity traps the energy of fusion more efficiently and results in a larger radius, cooler star. More efficient use of energy also means that nuclear burning can proceed more slowly, resulting in a longer lifetime for the star.”
The lifetime of a star’s habitable zone can also be influenced by another element – oxygen. Young continues: “The habitable lifetime of an orbit the size of Earth’s around a one-solar-mass star is only 3.5 billion years for oxygen-depleted compositions but 8.5 billion years for oxygen-rich stars. For comparison, we expect the Earth to remain habitable for another billion years or so, for about 5.5 billion years total, before the Sun becomes too luminous. Complex life on Earth arose some 3.9 billion years after its formation, so if Earth is at all representative, low-oxygen stars are perhaps less than ideal targets.”
As well as the habitable zone, the composition of a star can determine the eventual composition of any planets that form. The carbon-oxygen and magnesium-silicon ratios of stars can affect whether a planet will have magnesium or silicon-loaded clay minerals such as magnesium silicate (MgSiO3), silicon dioxide (SiO2), magnesium orthosilicate (Mg2SiO4), and magnesium oxide (MgO). A star’s composition can also play a role in whether a rocky planet might have carbon-based rock instead of silicon-based rock like our planet. Even the interior of planets could be affected, as radiocative elements would determine whether a planet has a molten core or a solid one. Plate tectonics, thought to be important for the evolution of life on Earth, depend on a molten interior.
Young and his team are now looking at 600 stars, ones that are already being targeted in exoplanet searches. They plan to produce a list of the 100 best stars which could have potentially habitable planets.
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At this time of year, after dark we in the northern hemisphere are able to see the mighty constellation of Orion rise high in the sky with a very bright companion in a nearby constellation: Sirius – The Dog Star.
Sirius is the brightest star in the sky and can easily be found in the faint constellation of Canis Major to the left and below Orion. Its name comes from ancient Greek meaning “glowing” or “scorcher.”
Sirius (α CMa) is the alpha star in this trusty hound and is roughly 8.5 light years away from Earth, making it one of the closest stars to us. It has a tiny companion star making it a binary system composed of “Sirius A” the main component (which is a white main sequence star) and “Sirius B,” a white dwarf star. As seen with the naked eye, Sirius can be seen to twinkle many different colours low in the winter evening sky. Sirius. Image credit: Hubble
So why does Sirius twinkle?
It’s not just Sirius that twinkles; all stars twinkle. Light travels many light years from stars and right at the end of its journey, it hits Earth’s atmosphere, which consists of nitrogen, oxygen and other gasses.
Earth’s atmosphere is constantly swirling around, and wind and air currents etc distort light travelling through it. This causes the light to slightly bend or shimmer and the light from distant stars twinkle. An extreme, more down-to-Earth example of this would be heat rising off of a road or a desert causing objects behind it to distort, shimmer and change colour.
Sirius appears to twinkle or shimmer more than other stars for some very simple reasons. It is very bright, which can amplify atmospheric effects and it is also very low down in the atmosphere for those in the northern hemisphere. We are actually looking at it through a very dense part of the atmosphere which can be turbulent and contain many different particles and dust. The lower towards the horizon an observer is looking, the thicker the atmosphere. The higher an observer is looking, the thinner the atmosphere. This is also the cause of colourful sunrise and sunsets.
(Addition due to the questions in the comment section: planets don’t usually twinkle because they are closer and therefore bigger — they are disks of light instead of faraway points of light. The larger disks of light usually aren’t distorted; however if you are looking through especially turbulent areas of our atmosphere, and even sometimes when looking at planets that are low in the thicker parts of the atmosphere, they will twinkle. Phil Plait, the Bad Astronomer explains it very well on his website.)
This optical illusion is a big pain for astronomers and some very large telescopes such as those in Chile and Hawaii use special equipment and techniques to reduce the effects of the atmosphere.
One of most famous telescope of them all, the Hubble Space Telescope doesn’t get affected at all by our atmosphere as it is in space, making the light from stars crystal clear.
Twinkle, twinkle little star, now we know what you are (and why you are twinkling!)
