Stellar Evolution Archives

September 25, 2014December 23, 2015 by Tammy Plotner

Hubble Vision: Galaxy DDO 68 – Young Or Old?

Only astronomers know for sure… Or do they? In this assembly of images taken with Hubble’s Advanced Camera for Surveys, scientists have utilized both visible and infrared light to survey a most unusual galaxy. When looking for a newly formed galaxy in our “cosmic neighborhood”, they spied DDO 68 (a.k.a. UGC 5340). Normally to witness galactic evolution, we have to look over great distances to see back in time… but this particular collection of gas and stars seems to break the rules!

Researching galactic evolution isn’t a new concept. Over the last few decades astronomers have increased our understanding of how galaxies change with time. One of the most crucial players in this game has been the NASA/ESA Hubble Space Telescope. Through its eyes, scientists can see over almost incomprehensible distances – studying light that has taken billions of years to reach us. We are essentially looking back in time.

While this is great news on its own, studying progressively younger galaxies can sometimes pose more questions than it answers. For example, all the newly created galaxies reside a huge distance from us and thereby appear small and faint when imaged. On the other side of the coin, galaxies which are close to us appear to be far more mature.

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This video begins with a ground based view of the night sky, before zooming in on dwarf galaxy DDO 68 as the NASA/ESA Hubble Space Telescope sees it. This ragged collection of stars and gas clouds looks at first glance like a recently-formed galaxy in our own cosmic neighbourhood. But, is it really as young as it looks? Credit: NASA/ESA

DDO 68, imaged here by the NASA/ESA Hubble Space Telescope, would seem to be the best example of a nearby newly-formed galaxy. Just how nearby? Estimates place it at about 39 million light years distant. While this might seem like a very long way, it is still roughly 50 times closer than other galactic examples. Studying galaxies of different ages is important to our understanding of how the Universe works. Astronomers have discovered that young galaxies are quite different than those which have aged. In this case, DDO 68 gives off the appearance of being young. These findings come from examining its structure, appearance and composition. However, researchers question their findings. It is possible this galaxy may be considerably older than initial findings indicate.

“All of the available data are consistent with the fact that DDO 68 is a very rare candidate for young galaxies.” says S. A. Pustilnik (et al). “The bulk of its stars were formed during the recent (with the first encounter about 1 Gyr ago) merger of two very gas-rich disks.”

These common events – mergers and collisions – are part of galactic life and are generally responsible for older galaxies being more bulky. These “senior citizens” are normally laced with a wide variety of stellar types – young, old, large and small. The chemistry is also different, too. Very young galaxies are rich in hydrogen and helium, making them tantalizingly similar in composition to the primordial matter created by the Big Bang. Older galaxies have more experiences. Numerous stellar events have happened within them over their lifetimes, making them rich in heavy elements. This is what makes DDO 68 very exciting! It is the best local candidate found so far to be low in heavier elements.

“DDO 68 (UGC 5340) is the second most metal-poor star-forming galaxy,” explains Pustilnik. “Its peculiar optical morphology and its HI distribution and kinematics are indicative of a merger origin. We use the u, g, r, and i photometry based on the SDSS images of DDO 68 to estimate its stellar population ages.”

Step into the light? You bet. The Hubble observations were meant to examine the properties of this mysterious galaxy’s light – determine whether or not it contains any older stars. If they are discovered, which seems to be the case, this would disprove the theory that DDO 68 is singularly comprised of younger stars. If not, it will validate the unique nature of this nearby neighbor. While more computer modeling and studies are needed, we can still enjoy this incredible look at another cosmic enigma!

Original Story Source: A Galaxy Of Deception – Hubble/ESA

September 24, 2014December 23, 2015 by Elizabeth Howell

Did Wild Weather — Or A Companion — Cause Eerie Infrared Glow From This Baby Star?

Artist's impression AS 205 N, which is a T Tauri star, and a smaller partner. Credit: P. Marenfeld (NOAO/AURA/NSF)

Watch out! Carbon monoxide gas is likely fleeing the disk of a young star like our Sun, producing an unusual signature in infrared. This could be the first time winds have been confirmed in association with a T Tauri star, or something else might be going on.

Because the observed signature of the star (called AS 205 N) didn’t meet what models of similar stars predicted, astronomers say it’s possible it’s not winds after all, but a companion tugging away at the gas.

“The material in the disk of a T Tauri star usually, but not always, emits infrared radiation with a predictable energy distribution,” stated Colette Salyk, an astronomer with the National Optical Astronomical Observatory who led the research. “Some T Tauri stars, however, like to act up by emitting infrared radiation in unexpected ways.”

View of the Atacama Large Millimeter/submillimeter Array (ALMA) site, which is 5,000 meters (16,400 feet) on the Chajnantor Plateau in the Atacama Desert of northern Chile. Credit: A. Marinkovic/X-Cam/ALMA (ESO/NAOJ/NRAO)

T Tauri stars are still young enough to be surrounded by dust and gas that could eventually form planets. Winds in the vicinity, however, could make it difficult for enough gas to stick around to form Jupiter-sized gas giants — or could change where planets are formed altogether.

While it’s still unclear what’s going on in AS 205 N, the astronomers plan to follow up their work with observing other T Tauri stars. Maybe with more observations, they reason, they can better understand what these signatures are telling us.

The weird environment was spotted by astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA), a set of 66 radio telescopes in Chile. A paper based on the research was published in the Astrophysical Journal and is also available in preprint version on Arxiv.

Source: National Radio Astronomy Observatory

September 12, 2014December 23, 2015 by Elizabeth Howell

Wow! Water Ice Clouds Suspected In Brown Dwarf Beyond The Solar System

Artist's conception of brown dwarf WISE J085510.83-071442.5, which may host water ice clouds in its atmosphere. Credit: Rob Gizis (CUNY BMCC / YouTube (screenshot)

What are planetary atmospheres made of? Figuring out the answer to that question is a big step on the road to learning about habitability, assuming that life tends to flourish in atmospheres like our own.

While there is a debate about how indicative the presence of, say, oxygen or water is of life on Earth-like planets, astronomers do agree more study is required to learn about the atmospheres of planets beyond our solar system.

Which is why this latest find is so exciting — one astronomy team says it may have spotted water ice clouds in a brown dwarf (an object between the size of a planet and a star) that is relatively close to our solar system. The find is tentative and also in an object that likely does not host life, but it’s hoped that telescopes may get better at examining atmospheres in the future.

The object is called WISE J085510.83-071442.5, or W0855 for short. It’s the coldest brown dwarf ever detected, with an average temperature between 225 degrees Kelvin (-55 Fahrenheit, or -48 Celsius) and 265 Kelvin (17 Fahrenheit, or -8 Celsius.) It’s believed to be about three to 10 times the mass of Jupiter.

Astronomers looked at W0855 with an infrared mosaic imager on the 6.5-meter Magellan Baade telescope, which is located at Las Campanas Observatory in Chile. The team obtained 151 images across three nights in May 2014.

Astronomers plotted the brown dwarf on a color-magnitude chart, which is a variant of famous Hertzsprung-Russell diagram used to learn more about stars by comparing their absolute magnitude against their spectral types. “Color-Magnitude diagrams are a tool for investigating atmospheric properties of the brown dwarf population as well as testing model predictions,” the authors wrote in their paper.

Based on previous work on brown dwarf atmospheres, the team plotted W0855 and modelled it, discovering it fell into a range that made water ice clouds possible. It should be noted here that water ice is known to exist in all four gas giants of our own Solar System: Jupiter, Saturn, Uranus, and Neptune.

“Non-equilibrium chemistry or non-solar metallicity may change predictions,” the authors cautioned in their paper. “However, using currently available model approaches, this is the first candidate outside our own solar system to have direct evidence for water clouds.”

The research, led by the Carnegie Institution for Science’s Jacqueline Faherty, was published in Astrophysical Journal Letters. A preprint version of the paper is available on Arxiv.

Source: Carnegie Institution for Science

August 29, 2014December 23, 2015 by Shannon Hall

Radio Telescopes Resolve Pleiades Distance Debate

An optical image of the Pleiades. Credit: NOAO / AURA / NSF

Fall will soon be at our doorstep. But before the leaves change colors and the smell of pumpkin fills our coffee shops, the Pleiades star cluster will mark the new season with its earlier presence in the night sky.

The delicate grouping of blue stars has been a prominent sight since antiquity. But in recent years, the cluster has also been the subject of an intense debate, marking a controversy that has troubled astronomers for more than a decade.

Now, a new measurement argues that the distance to the Pleiades star cluster measured by ESA’s Hipparcos satellite is decidedly wrong and that previous measurements from ground-based telescopes had it right all along.

The Pleiades star cluster is a perfect laboratory to study stellar evolution. Born from the same cloud of gas, all stars exhibit nearly identical ages and compositions, but vary in their mass. Accurate models, however, depend greatly on distance. So it’s critical that astronomers know the cluster’s distance precisely.

A well pinned down distance is also a perfect stepping stone in the cosmic distance ladder. In other words, accurate distances to the Pleiades will help produce accurate distances to the farthest galaxies.

With parallax technique, astronomers observe object at opposite ends of Earth's orbit around the Sun to precisely measure its distance. CREDIT: Alexandra Angelich, NRAO/AUI/NSF. — With the parallax technique, astronomers observe object at opposite ends of Earth’s orbit around the Sun to precisely measure its distance. Credit: Alexandra Angelich, NRAO / AUI / NSF

But accurately measuring the vast distances in space is tricky. A star’s trigonometric parallax — its tiny apparent shift against background stars caused by our moving vantage point — tells its distance more truly than any other method.

Originally the consensus was that the Pleiades are about 435 light-years from Earth. However, ESA’s Hipparcos satellite, launched in 1989 to precisely measure the positions and distances of thousands of stars using parallax, produced a distance measurement of only about 392 light-years, with an error of less than 1%.

“That may not seem like a huge difference, but, in order to fit the physical characteristics of the Pleiades stars, it challenged our general understanding of how stars form and evolve,” said lead author Carl Melis, of the University of California, San Diego, in a press release. “To fit the Hipparcos distance measurement, some astronomers even suggested that some type of new and unknown physics had to be at work in such young stars.”

If the cluster really was 10% closer than everyone had thought, then the stars must be intrinsically dimmer than stellar models suggested. A debate ensued as to whether the spacecraft or the models were at fault.

To solve the discrepancy, Melis and his colleagues used a new technique known as very-long-baseline radio interferometry. By linking distant telescopes together, astronomers generate a virtual telescope, with a data-gathering surface as large as the distances between the telescopes.

The network included the Very Long Baseline Array (a system of 10 radio telescopes ranging from Hawaii to the Virgin Islands), the Green Bank Telescope in West Virginia, the William E. Gordon Telescope at the Arecibo Observatory in Puerto Rico, and the Effelsberg Radio Telescope in Germany.

“Using these telescopes working together, we had the equivalent of a telescope the size of the Earth,” said Amy Miouduszewski, of the National Radio Astronomy Observatory (NRAO). “That gave us the ability to make extremely accurate position measurements — the equivalent of measuring the thickness of a quarter in Los Angeles as seen from New York.”

After a year and a half of observations, the team determined a distance of 444.0 light-years to within 1% — matching the results from previous ground-based observations and not the Hipparcos satellite.

“The question now is what happened to Hipparcos?” Melis said.

The spacecraft measured the position of roughly 120,000 nearby stars and — in principle — calculated distances that were far more precise than possible with ground-based telescopes. If this result holds up, astronomers will grapple with why the Hipparcos observations misjudged the distances so badly.

ESA’s long-awaited Gaia observatory, which launched on Dec. 19, 2013, will use similar technology to measure the distances of about one billion stars. Although it’s now ready to begin its science mission, the mission team will have to take special care, utilizing the work of ground-based radio telescopes in order to ensure their measurements are accurate.

The findings have been published in the Aug. 29 issue of Science and is available online.

August 27, 2014December 23, 2015 by Shannon Hall

Fingerprint From a First-Generation Star?

SDSS001820.5-093939.2 (seen in white) is a small, second-generation star bearing the chemical imprint of one of the universe's first stars. It shines at an apparent magnitude of 15.8, just south of the celestial equator in the constellation Cetus. Credit: SDSS / NAO

The young universe was composed of a pristine mix of hydrogen, helium, and a tiny trace of lithium. But after hundreds of millions of years, it began to cool and giant clouds of the primordial elements collapsed to form the first stars.

The first “Population III” stars were extremely massive and bright, synthesizing the first batches of heavy elements, and erupting as supernovae after relatively short lifetimes of just a few million years. This cycle of star birth and death has steadily produced and dispersed more heavy elements throughout cosmic history.

Astronomers haven’t spotted any of the first stars still shining today. But now, a team using the 8.2-meter Subaru Telescope has discovered an ancient low-mass star that likely formed from the elements produced in the supernova explosion of a very massive first generation star.

Pop III stars with masses exceeding 100 times that of the Sun would have died in a peculiar explosion that theorists call a pair-instability supernova.

Like its lower-energy comrade, a pair-instability supernova occurs when a massive star no longer produces enough energy to counteract the inward pull of gravity. But with so much mass, the star’s core is squeezed to such a high temperature and pressure that runaway nuclear reactions power a devastating explosion. The whole star is obliterated and no compact remnant, such as a black hole or neutron star, is left behind.

Astronomers have seen hints of these rare events before. But now, Wako Aoiki from the National Astronomical Observatory of Japan and colleagues have approached the search in a different way, by finding a star that bears the chemical fingerprints of these ancient explosions.

The elements we see lacing a star’s surface provide a key to understanding the supernova that preceded the star’s birth. And the star, dubbed SDSS001820.5-093939.2, exhibits a peculiar set of chemical abundance ratios. It has high levels of heavy elements, such as nickel, calcium, and iron, but low levels of light elements, such as carbon, magnesium and cobalt.

Note that the star is still metal poor in the grand scheme of things. Its iron abundance is 1/100 of the solar level. But compared with most metal-poor stars, where the iron abundance can be 1/100,000 or less of the solar level, the star is metal rich.

The chemical abundance ratios (with respect to iron) of SDSS J0018-0939 (red circles) compared with model prediction for explosions of very-massive stars. The black line indicates the model of a pair-instability supernova by a star with 300 solar masses, whereas the blue line shows the model of an explosion caused by a core-collapse of a star with 1000 solar masses. The abundance ratios of sodium (Na) and aluminum (Al), which are not well-reproduced by these models, might be produced during the evolution of stars before the explosion, but that is not included in the current model. (Credit: NAOJ)

These odd fingerprints suggest the star formed from material seeded by the death of a very massive Pop III star. In fact, the chemical composition of the star matches the elements that pair-instability supernovae are predicted to create.

The team notes that this is the only star of about 500 in the same low-metallicity range that has this peculiar makeup. It is — at the moment — our only window into the early universe and the first generation of stars.

The paper was published Aug. 22 in Science and is available online.

August 27, 2014December 23, 2015 by Elizabeth Howell

Weird X-Rays: What Happens When Eta Carinae’s Massive Stars Get Close?

Eta Carinae, one of the most massive stars known. Image credit: NASA — Eta Carinae, one of the most massive stars known. Credit: NASA

While the stars appear unchanging when you take a quick look at the night sky, there is so much variability out there that astronomers will be busy forever. One prominent example is Eta Carinae, a star system that erupted in the 19th century for about 20 years, becoming one of the brightest stars you could see in the night sky. It’s so volatile that it’s a high candidate for a supernova.

The two stars came again to their closest approach this month, under the watchful eye of the Chandra X-Ray Observatory. The observations are to figure out a puzzling dip in X-ray emissions from Eta Carinae that happen during every close encounter, including one observed in 2009.

The two stars orbit in a 5.5-year orbit, and even the lesser of them is massive — about 30 times the mass of the Sun. Winds are flowing rapidly from both of the stars, crashing into each other and creating a bow shock that makes the gas between the stars hotter. This is where the X-rays come from.

Here’s where things get interesting: as the stars orbit around each other, their distance changes by a factor of 20. This means that the wind crashes differently depending on how close the stars are to each other. Surprisingly, the X-rays drop off when the stars are at their closest approach, which was studied closely by Chandra when that last occurred in 2009.

Eta Carinae shines brightly in X-rays in this image from the Chandra X-Ray Observatory.

“The study suggests that part of the reason for the dip at periastron is that X-rays from the apex are blocked by the dense wind from the more massive star in Eta Carinae, or perhaps by the surface of the star itself,” a Chandra press release stated.

“Another factor responsible for the X-ray dip is that the shock wave appears to be disrupted near periastron, possibly because of faster cooling of the gas due to increased density, and/or a decrease in the strength of the companion star’s wind because of extra ultraviolet radiation from the massive star reaching it.”

More observations are needed, so researchers are eagerly looking forward to finding out what Chandra dug up in the latest observations. A research paper on this was published earlier this year in the Astrophysical Journal, which you can also read in preprint version on Arxiv. The work was led by Kenji Hamaguchi, who is with NASA’s Goddard Space Flight Center in Maryland.

Source: Chandra X-Ray Observatory

August 15, 2014December 23, 2015 by Elizabeth Howell

What Sparked Star Explosion 2014J? NASA Telescope Seeks Clues

Astronomers are gazing closely at supernova 2014J (inset) to see what sort of triggers caused the star explosion. Credit: NASA/SAO/CXC/R. Margutti et al

X marks the spot: after probing the area where a star used to be, in X-rays, astronomers have been able to rule out one cause for the supernova explosion.

Because the Chandra X-Ray Observatory did not detect anything unusual in X-rays, astronomers say this means that a white dwarf was not responsible for pulling off material from a massive star that exploded (from Earth’s vantage point) on Jan. 21, 2014, triggering excitement from professional and amateur astronomers alike.

“While it may sound a bit odd, we actually learned a great deal about this supernova by detecting absolutely nothing,” stated study leader Raffaella Margutti of the Harvard-Smithsonian Center for Astrophysics (CfA) in Massachusetts. “Now we can essentially rule out that the explosion was caused by a white dwarf continuously pulling material from a companion star.”

So what caused it? Possibly two white dwarfs merged instead. Follow-up observations will take place in Messier 88 and the source of the explosion, which was about 12 million light-years from Earth. While that’s a long time by human standards, astronomers point out that is close on the cosmic distance scale.

A study on this work was recently published in The Astrophysical Journal. You can read a preprint version of the article here.

Source: NASA

August 14, 2014December 23, 2015 by Elizabeth Howell

Diamond Pinpricks: Gorgeous Shot Of Star Group That Once Baffled Astronomers

A Hubble Space Telecope picture of globular cluster IC 4499. The new observations showed that it is about 12 billion years old, contrary to previous observations showing a puzzling young age. Credit: European Space Agency and NASA

Is this group of stars belonging to one generation, or more? That’s one of the things that was puzzling astronomers for decades, particularly when they were trying to pin down the age of IC 4499 — the globular cluster you see in this new picture from the Hubble Space Telescope.

While astronomers now know the stars are from a single generation that are about 12 billion years old (see this paper from three years ago), for about 15 years before that at least one paper said IC 4499 was three billion to four billion years younger than that.

“It has long been believed that all the stars within a globular cluster form at the about same time, a property which can be used to determine the cluster’s age,” stated information from the European Space Agency reposted on NASA’s website.

“For more massive globulars however, detailed observations have shown that this is not entirely true — there is evidence that they instead consist of multiple populations of stars born at different times.”

IC 4499 is somewhere in between these extremes, but only has a single generation of stars — its gravity wasn’t quite enough to pull in neighboring gas and dust to create more. Goes to show you how important it is to re-examine the results in science.

Source: NASA and the European Space Agency

August 5, 2014December 23, 2015 by Elizabeth Howell

Can A ‘Planet-Like Object’ Start Its Life Blazing As Hot As A Star?

How WISE 70304-2705 could have evolved from a star to a "planet-like object". Credit: John Pinfield,

Nature once again shows us how hard it is to fit astronomical objects into categories. An examination of a so-far unique brown dwarf — an object that is a little too small to start nuclear fusion and be a star — shows that it could have been as hot as a star in the ancient past.

The object is one of a handful of brown dwarfs that are called “Y dwarfs”. This is the coolest kind of star or star-like object we know of. These objects have been observed at least as far back as 2008, although they were predicted by theory before.

A group of scientists observed the object, called WISE J0304-2705, with NASA’s space-based Wide-field Infrared Survey Explorer (WISE). Looking at the spectrum of light it had emitted, which shows the object’s composition, has scientists saying that what the brown dwarf is made of suggests it is rather old — billions of years old.

“Our measurements suggest that this Y dwarf may have a composition … or age characteristic of one of the galaxy’s older members,” stated David Pinfield at the University of Hertfordshire, who led the research.

“This would mean its temperature evolution could have been rather extreme – despite starting out at thousands of degrees, this exotic object is now barely hot enough to boil a cup of tea.”

Size comparison of stellar vs substellar objects. (Credit: NASA/JPL-Caltech/UCB).

While the object started out hot, its interior never was quite enough to fuse hydrogen. That led to the extreme cooling visible today.

Models suggest the object would have begun its life shining at 2,800 degrees Celsius (5,072 Fahrenheit), for a phase that would have lasted for 20 million years. In the next 100 million years, its temperature would have almost halved to 1,500 Celsius (2,730 Fahrenheit).

And it would have kept cooling, with a temperature of 1,000 Celsius (1,832 Fahrenheit) after a billion years, and after billions of more years, the temperature we see today — somewhere between 100 Celsius (212 Fahrenheit) and 150 Celsius (302 Fahrenheit).

The paper will be published shortly in the Monthly Notices of the Royal Astronomical Society. The research is available in preprint version on Arxiv. One limitation of the research is the small number of Y dwarfs discovered, only about 20, which means that more observations will be needed to see if other objects could have had this same evolution.

Source: Royal Astronomical Society

August 4, 2014December 23, 2015 by Nancy Atkinson

Deep Astrophoto of LDN 673: The Place Where Stars are Born

LDN 673, a molecular cloud complex in the constellation Aquila. Credit and copyright: Callum Hayton.

What a stunning view of this dark region of space! This image, by astrophotographer Callum Hayton shows LDN 673, a molecular cloud complex that lies in the constellation Aquila. This region is massive — around 67 trillion kilometers (42 trillion miles across), and it is between 300-600 light years from Earth. Observers in the northern hemisphere can find this region in the summer skies near the bright star Altair and the Summer Triangle.

Because the cloud lies on the galactic plane, the dark dust is back-lit by millions of stars in the Milky Way galaxy. This dusty cloud likely contains enough raw material to form hundreds of thousands of stars. Hayton explained on Flickr how the dust gets “eroded” away by stellar formation:

“When some of these clouds reach a certain mass they begin to collapse and fragment creating protostars,” Hayton wrote. “As the temperature and pressure at the centre of the protostar rises, sometimes it becomes so great that nuclear fusion begins and a star is born. In this image you can see where at least two young stars have eroded the dust around them and are now above the clouds casting light down on to the dust below.”

Gorgeous!

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