astrophysics Archives - Page 3 of 13 - The Spacewriter's Ramblings

Monday, January 5, 2009

Astronomy is truly a science that takes you places. At one level, it has brought ME to Long Beach, CA to hear about the latest and greatest astronomy discoveries. At another level, it is bringing us (scientists, writers — and ultimately our audiences) out to the most fascinating places in the cosmos.

“Where?” you ask. How about the core of the Milky Way Galaxy? Q.D. Wang of the University of Massachusetts at Amherst used the Hubble Space Telescope to make an infrared mosaic of the center of our galaxy. It’s a beautiful panoramic view that takes in an area of space measuring 300 x 150 light-years.

The core of the Milky Way in an infrared mosaic from Hubble Space Telescope. (click to embiggen)

This is a “false-color” image taken through a filter that reveals the glow of hydrogen gas heated by winds from new stars revealed as a new population of massive stars at the core. And the cool thing is that this is the sharpest infrared picture ever made of the galactic core.

Astronomers are looking at this region to understand how massive stars form and what they do to their local enviroment during their tempestuous birth process. If we can understand how it works in OUR galaxy then we have insight into how it works in the cores of other galaxies, particularly the active ones. Read more about this fascinating image at at the Space Telescope web site.

This 0.6 by 0.7-degree infrared photograph of the galactic center shows a large population of old, red stars. However, the discovery of two young protostars within a few light-years of the center of the Milky Way shows that stars can form there despite powerful gravitational tides due to the supermassive black hole. Credit: 2MASS/E. Kopan (IPAC/Caltech)

Now, looking at the center of the galaxy is difficult, since it’s shrouded in dust clouds. The good news is that we can plumb those depths using infrared and radio telescopes. Astronomers at Harvard-Smithsonian Center for Astrophysics and the Max Planck Institute for Radio Astronomy have used the Very Large Array in New Mexico to study young stars that really shouldn’t be there.

This is because the core of the galaxy is not a gentle creche where young stars should be able to form. It’s wracked with powerful radiation and gravitational tides stirred up by the four-million-solar-mass black hole that’s hidden at the core. It’s a place where stars go to get gobbled up, not get born.

So, nobody’s sure how a pair of protostars started to form at a spot only a few light-years from the galactic center. What this tells us is that this place, as wild as it might be, can still nurture star formation. Now astronomers will spend time figuring out how and why this is happening.

Artist's Conception of our Milky Way Galaxy: Blue, green dots indicate distance measurements. CREDIT: Robert Hurt, IPAC; Mark Reid, CfA, NRAO/AUI/NSF

This scenario may suggest that star-forming clouds may be much denser than we thought. For more information, check out the story here.

Continuing our look at the Milky Way, the folks at the National Radio Astronomy Observatory are looking at our galaxy using the Very Long Baseline Array radio telescope and what they’re finding is redefining what we know about our galactic home. Essentially, the Milky Way is rotating faster, is heavier, and is more likely to collide with other galaxies than we used to think.

You can read more about their findings at the link above, but just to give you an example of what they’ve found: at our location in the galaxy — some 28,000 light-years away from the core of the galaxy — we’re speeding along at 960,000 kilometers per hour (600,000 miles an hour).

An asteroid bites the dust around white dwarf star.

A little closer to home, astronomers continue to focus attention (and detectors) on exoplanets — worlds circling other stars.

The white dwarf GD40 and five other similar type stars came in for some attention by Mike Jura of the University of California, who used the Spitzer Space Telescope to study the remains of asteroids chewed up as the stars went through their red giant phase and then shrank down to become a white dwarf. That chewing action generated dust, which can be spotted with infrared-sensitive detectors. A star with MORE dust around it is “brighter” in infrared than a star with NO dust.

Ultimately, what their research suggests is that the same materials that made up our planet and other rocky worlds may be pretty common in the galaxy and the universe. You can read more about their work here.

NGC 2362 This photograph from NASAs Spitzer Space Telescope shows the young star cluster NGC 2362. By studying it, astronomers found that gas giant planet formation happens very rapidly and efficiently, within less than 5 million years, meaning that Jupiter-like worlds experience a growth spurt in their infancy. Credit: NASA/JPL-Caltech/T. Currie (CfA) — NGC 2362 This photograph from NASA's Spitzer Space Telescope shows the young star cluster NGC 2362. By studying it, astronomers found that gas giant planet formation happens very rapidly and efficiently, within less than 5 million years, meaning that Jupiter-like worlds experience a growth spurt in their infancy. Credit: NASA/JPL-Caltech/T. Currie (CfA)

One of the more intriguing stories is about how baby Jupiters form around other stars.

It turns out that, according to scientists at the Harvard-Smithsonian Center for Astrophysics (who used the Spitzer Space Telescope to look at stars in the cluster NGC 2362 to detect infrared signatures of active planetary formation) a Jupiter-type planet has a pretty short time frame to form before the dynamics of the system shut off the process.

For our solar system, that means that Jupiter took only 2 to 3 million years to spring into being, whereas Earth took 20 to 30 million years to aggregate and solidify. Read more here.

Finally (for now, anyway), I got a press release detailing the upcoming WISE mission, which will provide a highly detailed all-sky survey in the infrared, from 3 to 25 microns. It’s supposed to launch in 2009 and will map the sky for at least seven months. The scientists who use this instrument hope to find the most luminous galaxies in the universe, find the closest stars to the Sun, detect most of the asteroids in the Main Belt, and do a number of different studies of planetary discs around other stars.

Check out the WISE web site for more details.

Okay, there’s more to come, so stay tuned!

Two New Finds about our Galaxy

I was Born Near a Wanderin’ Star

The hardest galaxy to study in the universe is our own. We’re inside it, and just like trying to figure out the color of a building from a room within it, it’s tough for us to see the shape and density of our galactic home while being stuck inside of it. We have to use indirect evidence to infer galaxy characteristics for the Milky Way. Surveys of stars, particularly those done using infrared-sensitive instruments, tell us a lot about the distribution of stars and other mass in our galaxy. That’s because infrared astronomy lets us peer through the dark clouds and dusty regions of our galaxy, and we can study the chemical distribution of stars throughout the galaxy.

And, from those data sets, we can extrapolate to the areas of the galaxy we can’t see in optical wavelengths of light. We can make models using real data, and challenge long-held suppositions about the state of our galaxy and the stars it contains.

One such long-standing scientific theory holds that stars tend to hang out in the roughly the same galactic neighborhood where they were born. Some astrophysicists decided to look into whether that theory is true, and their simulations show that, at least in galaxies similar to our own Milky Way, stars such as the Sun can migrate great distances from their birthplaces.

If the Sun has actually fled the old ‘hood, that tells us that perhaps there are many regions in galaxies where stars that support planets — and life — could exist in reasonable safety (so-called “habitable zones”).

The group of astrophysicists, led by Rok Roskar, a grad student at the University of Washington, used more than 100,000 hours of computer cluster time at UW and the University of Texas supercomputer site (which I had a chance to visit earlier this year), to simulate the formation and evolution of a galaxy disk from material that had swirled together 4 billion years after the Big Bang.

The orbits of some stars in the galaxies might get larger or smaller but tend to remain very circular after hitting a massive spiral density wave that propagates through the arms of a galaxy. The Sun has a nearly circular orbit, so the findings mean that when it formed 4.59 billion years ago (about 50 million years before Earth did), it could have been either nearer to or farther from the center of the galaxy, rather than halfway toward the outer edge where it is now. As it encountered the density waves that accompany the spiral arms, its orbit around the galaxy would have been shaped by the encounters.

Migrating stars also help explain a long-standing problem in understanding the chemical mix of stars in the neighborhood of our solar system. Simply put, our region of the galaxy has long been known to be more mixed and diluted than you might expect if our stellar neighbors had spent their entire lives where they were born. It makes sense when you think about it: if a given star cloud births many new stars, they’ll all have the same (roughly) chemical composition because they all come from the same cloud. Any stars with different chemical abundances would have to be from another star cloud, maybe one quite far away. If stars from different locations have migrated here, then the Sun’s neighborhood has become a more diverse and interesting place over the past few billion years.

The scientists plan to run a range of simulations with varying physical properties to generate different kinds of galactic disks, and then determine whether stars show similar ability to migrate large distances within different types of disk galaxies.

Things that Shape Galaxies in the Dark

Stars are the “small-scale” matter that inhabits galaxies. The galaxies themselves (the giant mass of stars, dust clouds, and so forth) are shaped by much larger forces than the wanderings of stars over galactic time. The large-scale evolution of a galaxy and its shape (its morphology) appears to be influenced by dark matter. At least, that’s the current thought, and as scientists find more evidence of dark matter, they are starting to get a clearer picture of its distribution and the effect it has on galaxy morphology.

Unlike the stars, gas and dust that make up what scientists call “baryonic” or “normal” matter, dark matter is invisible. We know its there because it has a gravitational influence on its surroundings. Physicists suspect that it makes up 22% of the mass of the universe (compared with the 4% of normal matter and 74% comprising the mysterious ‘dark energy’). But, despite the fact that it seems to be everwhere, no one is sure what dark matter consists of.)

A computer simulation of the disk of dark matter in the Milky Way Galaxy. This composite image shows the dark matter disk (in red) and an Atlas image mosaic of the Milky Way made as part of the 2-Micron All Sky Survey (2MASS). By J. Read and O. Agertz.

Today, an international team of scientists is predicting that the Milky Way contains a disk of dark matter. In a paper published in Monthly Notices of the Royal Astronomical Society, astronomers Justin Read, George Lake and Oscar Agertz of the University of Zurich, and Victor Debattista of the University of Central Lancashire used the results of a supercomputer simulation to infer the presence of this disk; they haven’t directly imaged it, they are deducing its existence from its effects on nearby matter and then using their work to create a computer simulation of the galaxy and disk. This simulation could allow physicists to directly detect and identify the nature of dark matter for the first time.

How Does this Work?

For a long time, scientists thought that dark matter forms in roughly spherical lumps called “halos” that envelope galaxies. There is one that surrounds the Milky Way. However, this “standard’ theory is based on supercomputer simulations that model the gravitational influence of the dark matter alone. The new simulation takes into account the gravitational influence of the stars and gas that also make up our galaxy.

Stars and gas are thought to have settled into disks very early on in the life of the universe and this affected how smaller dark matter halos formed. The team’s results suggest that most lumps of dark matter in our local galactic neighborhood merged to form a halo around the Milky Way. But the largest lumps were preferentially dragged towards the galactic disk and were then torn apart. This is what likely created the disk of dark matter within the galaxy.

Detecting the two different dark matter components depends on the density of each, according to Justin Read, the lead scientist on this project. “The dark disk only has about half of the density of the dark matter halo, which is why no one has spotted it before,” he says. “However, despite its low density, if the disk exists it has dramatic implications for the detection of dark matter here on Earth.

The Earth and Sun move at some 220 kilometers per second along a nearly circular orbit about the center of the galaxy. The dark matter halo does not rotate. This means that if we could see the dark matter halo as we rotated through the galaxy, it would appear as if we had a “wind” of dark matter flowing towards us at great speed. By contrast, the disk of dark-matter particles rotates along with us, and so the “wind” from the dark disk is much slower.

This abundance of low-speed dark matter particles could be a real boon for researchers because they are more likely to excite a response in dark matter detectors than fast-moving particles. Is there such a detector? Yes–it’s called XENON (located at the Gran Sasso Underground Laboratory in Italy) and it’s built to directly detect dark matter particles. This detector is very sensitive, and if there’s dark matter out there, particularly the low-speed type in the suggested disk, XENON should be able to see it. This new research raises the exciting prospect that the dark disk of our galaxy and its associated dark matter could be directly detected in the very near future. Will it tell us what dark matter is made of? Let’s hope so!

******************

The Spacewriter's Ramblings

Category Archives: astrophysics

Dispatches from the Cosmos

Monday, January 5, 2009

Focus on The Milky Way Galaxy

Two New Finds about our Galaxy

Exploring Science and the Cosmos