Universe Today

Image source: CfA

According to cosmologists, the early Universe only had a mixture of hydrogen, helium and other lighter elements, but none of the heaver elements required for life – like carbon. From the original gasses, giant stars formed – some were 200 times larger than our Sun – lived for a brief time, often just a few million years. These giant stars converted up to 50% of their material into heaver elements, mostly iron, before exploding violently as supernovae. The James Webb telescope, due for launch after 2011 will be so sensitive it should be able to look back to watch these supernovae happening.

The early universe was a barren wasteland of hydrogen, helium, and a touch of lithium, containing none of the elements necessary for life as we know it. From those primordial gases were born giant stars 200 times as massive as the Sun, burning their fuel at such a prodigious rate that they lived for only about 3 million years before exploding. Those explosions spewed elements like carbon, oxygen and iron into the void at tremendous speeds. New simulations by astrophysicists Volker Bromm (Harvard-Smithsonian Center for Astrophysics), Naoki Yoshida (National Astronomical Observatory of Japan) and Lars Hernquist (CfA) show that the first, “greatest generation” of stars spread incredible amounts of such heavy elements across thousands of light-years of space, thereby seeding the cosmos with the stuff of life.

This research is posted online at http://arxiv.org/abs/astro-ph/0305333 and will be published in an upcoming issue of The Astrophysical Journal Letters.

“We were surprised by how violent the first supernova explosions were,” says Bromm. “A universe that was in a pristine state of tranquility was rapidly and irreversibly transformed by a colossal input of energy and heavy elements, setting the stage for the long cosmic evolution that eventually led to life and intelligent beings like us.”

Approximately 200 million years after the Big Bang, the universe underwent a dramatic burst of star formation. Those first stars were massive and fast-burning, quickly fusing their hydrogen fuel into heavier elements like carbon and oxygen. Nearing the end of their lives, desperate for energy, those stars burned carbon and oxygen to form heavier and heavier elements until reaching the end of the line with iron. Since iron cannot be fused to create energy, the first stars then exploded as supernovae, blasting the elements that they had formed into space.

Each of those first giant stars converted about half of its mass into heavy elements, much of it iron. As a result, each supernova hurled up to 100 solar masses of iron into the interstellar medium. The death throes of each star added to the interstellar bounty. Hence, by the remarkably young age of 275 million years, the universe was substantially seeded with metals.

That seeding process was aided by the structure of the infant universe, where small protogalaxies less than one-millionth the mass of the Milky Way crammed together like people on a crowded subway car. The small sizes of and distances between those protogalaxies allowed an individual supernova to rapidly seed a significant volume of space.

Supercomputer simulations by Bromm, Yoshida, and Hernquist showed that the most energetic supernova explosions sent out shock waves that flung heavy elements up to 3,000 light-years away. Those shock waves swept huge amounts of gas into intergalactic space, leaving behind hot “bubbles,” and triggered new rounds of star formation.

Supernova expert Robert Kirshner (CfA) says, “Today this is a fascinating theory, based on our best understanding of how the first stars worked. In a few years, when we build the James Webb Space Telescope, the successor to the Hubble Space Telescope, we should be able to see these first supernovae and test Volker’s ideas. Stay tuned!”

Lars Hernquist notes that the second generation of stars contained heavy elements from the first generation – seeds from which rocky planets like Earth could grow. “Without that first, ‘greatest generation’ of stars, our world would not exist.”

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Original Source: CfA News Release

Image credit: Hubble

It turns out that a collection of stars orbiting the Andromeda galaxy are actually the remnants of another galaxy being torn apart and consumed, according to new research from astronomers at Case University. They only realized it was a separate galaxy after charting the velocities of several of its stars. Astronomers failed to detect it before now because much of the galaxy is located in front of Andromeda’s bright galactic disk. The discovery will give astronomers further evidence to support the theory that smaller galaxies merge together to form larger, more complex galaxies.

Case Western Reserve University astronomers have announced the discovery of a new galaxy, termed Andromeda VIII. The new galaxy is so widespread and transparent that astronomers did not suspect its existence until they mapped the velocity of stars thought to belong to the well-known and nearby large Andromeda spiral galaxy and found them to move independently of Andromeda.

Heather Morrison, Paul Harding and Denise Hurley-Keller of Case’s department of astronomy and George Jacoby of the WIYN Observatory, will report their discovery in an upcoming article in Astrophysical Journal Letters.

“This is particularly exciting because it allows us to watch the ongoing growth of the nearby Andromeda galaxy from smaller galaxies,” says Morrison.

The astronomers used Case’s Burrell Schmidt telescope and the 3.5m WIYN telescope to identify the galaxy. Both telescopes are located at Kitt Peak National Observatory near Tucson, Ariz. NOAO is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a cooperative agreement with the National Science Foundation.

The newly found galaxy is being torn apart into streams of stars, which leaves a trail of stars that are strung out along the new galaxy’s orbit around the Andromeda galaxy in the way a jet’s contrail shows its route. Andromeda is the nearest large spiral galaxy to our own Milky Way galaxy two million light years away. It is visible as a hazy glowing object to the naked eye in a dark sky in the northern hemisphere and is found in the constellation of Andromeda.

Discovered over 1,000 years ago by the Persian astronomer Azophi Al-Sufi, Andromeda is a member of the Local Group of approximately 30 galaxies in the Milky Way’s celestial backyard.

In early August, Morrison finished analyzing the data of these stars from the Andromeda celestial neighborhood. “I was amazed to find a new dwarf galaxy orbiting Andromeda. It is a ‘see-thru’ galaxy, which was only discovered once we obtained velocity measurements for some of its stars, said Morrison.

She adds that the reason Andromeda VIII escaped detection was the fact that it is located in front of the bright regions of Andromeda’s galaxy disk.

Andromeda VIII’s total brightness is comparable to that of Andromeda’s well-known companion M32, a small nearby galaxy, but Andromeda VIII is spread over an area of the sky as much as ten times or more larger than M32. Its elongated shape is caused by Andromeda’s gravitational pull,
which has stretched it out due to the stronger gravity on the side nearest Andromeda.

Morrison and her collaborators also suggested that a very faint stream of stars, detected near the large Andromeda galaxy in 2001 by the Italian Astronmer R. A. Ibata and colleagues, was pulled off Andromeda VIII in an earlier passage around the parent galaxy. “Future research in this area should provide rich and fruitful results,” stated Morrison.

Theory has predicted for decades that galaxies are assembled in a “bottom-up” process, forming first as small galaxies that later merge to form large ones.

“Since 1994, when Ibata and colleagues announced the discovery of a new satellite in the process of being swallowed by the Milky Way, we have been able to see the process taking place in our own galaxy,” stated Morrison. “Now we find the same process in our nearest large neighbor.”

She adds that now it looks like Andromeda is even more inundated by small galaxies than the Milky Way. Ibata and colleagues have taken deep images of Andromeda which show a rich collection of star streams wreathed about the galaxy. Morrison and her colleagues have now identified the source of one of these star streams. They plan future observations to connect the different star streams with their progenitors, and thus learn more about the properties of the companion galaxy, the Andromeda galaxy and its elusive dark matter halo, the unseen matter that is suspected to be present in the universe.

The galaxy research was supported by a five-year National Science Foundation Early Career Development Award.

The Burrell Schmidt telescope is part of Case’s Warner and Swasey Observatory. The WIYN 3.5-meter telescope is a partnership of the University of Wisconsin, Indiana University, Yale University and the National Optical Astronomy Observatory (NOAO). NOAO is operated by the Association of Universities for Research in Astronomy (AURA) Inc., under a cooperative agreement with the National Science Foundation.

Original Source: NSF News Release

Image credit: Hubble

Astronomers have studied the light from 11 new supernovae to help validate the evidence that some kind of “dark energy” is accelerating the Universe apart. The supernovae are a special type called Ia, which are known to be roughly the same brightness. By measuring their relative brightness, they can calculate how distant the Type Ia supernovae are. This latest data was gathered by an international team of astronomers using ground telescopes to provide followup targets for the Hubble Space Telescope. A new satellite is planned, called the SuperNova/Acceleration Probe, which will be able to discover thousands of supernova and track their explosions precisely.

A unique set of 11 distant Type Ia supernovae studied with the Hubble Space Telescope sheds new light on dark energy, according to the latest findings of the Supernova Cosmology Project (SCP), recently posted at http://www.arxiv.org/abs/astro-ph/0309368 and soon to appear in the Astrophysical Journal.

Light curves and spectra from the 11 distant supernovae constitute “a strikingly beautiful data set, the largest such set collected solely from space,” says Saul Perlmutter, an astrophysicist at Lawrence Berkeley National Laboratory and leader of the SCP. The SCP is an international collaboration of researchers from the United States, Sweden, France, the United Kingdom, Chile, Japan, and Spain.

Type Ia supernovae are among astronomy’s best “standard candles,” so similar that their brightness provides a dependable gauge of their distance, and so bright they are visible billions of light years away.

The new study reinforces the remarkable discovery, announced by the Supernova Cosmology Project early in 1998, that the expansion of the universe is accelerating due to a mysterious energy that pervades all space. That finding was based on data from over three dozen Type Ia supernovae, all but one of them observed from the ground. A competing group, the High-Z Supernova Search Team, independently announced strikingly consistent results, based on an additional 14 supernovae, also predominantly observed from the ground.

Because the Hubble Space Telescope (HST) is unaffected by the atmosphere, its images of supernovae are much sharper and stronger and provide much better measurements of brightness than are possible from the ground. Robert A. Knop, assistant professor of physics and astronomy at Vanderbilt University in Nashville, Tenn., led the Supernova Cosmology Project’s data analysis of the 11 supernovae studied with the HST and coauthored the Astrophysical Journal report with the 47 other members of the SCP.

“The HST data also provide a strong test of host-galaxy extinction,” Knop says, referring to concerns that measurements of the true brightness of supernovae could be thrown off by dust in distant galaxies, which might absorb and scatter their light. But dust would also make a supernova’s light redder, much as our sun looks redder at sunset because of dust in the atmosphere. Because the data from space show no anomalous reddening with distance, Knop says, the supernovae “pass the test with flying colors.”

“Limiting such uncertainties is crucial for using supernovae ? or any other astronomical observations ? to explore the nature of the universe,” says Ariel Goobar, a member of SCP and a professor of particle astrophysics at Stockholm University in Sweden. The extinction test, says Goobar, “eliminates any concern that ordinary host-galaxy dust could be a source of bias for these cosmological results at high-redshifts.” (See What is Host-Galaxy Extinction?)

The term for the mysterious “repulsive gravity” that drives the universe to expand ever faster is dark energy. The new data are able to provide much tighter estimates of the relative density of matter and dark energy in the universe: under straightforward assumptions, 25 percent of the composition of the universe is matter of all types, and 75 percent is dark energy. Moreover, the new data provide a more precise measure of the “springiness” of the dark energy, the pressure that it applies to the universe’s expansion per unit of density.

Among the numerous attempts to explain the nature of dark energy, some are allowed by these new measurements ? including the cosmological constant originally proposed by Albert Einstein ? but others are ruled out, including some of the simplest models of the theories known as quintessence. (See What is Dark Energy?)

High-redshift supernovae are the best single tool for measuring the properties of dark energy ? and eventually determining what dark energy is. As supernova studies with the HST demonstrate, the best place to study high-redshift supernovae is with a telescope in space, unaffected by the atmosphere.

Nevertheless, “to make the best use of a telescope in space, it’s essential to make the best use of the finest telescopes on the ground,” says SCP member Chris Lidman of the European Southern Observatory.

For the supernovae in the present study, the SCP team invented a strategy whereby the Hubble Space Telescope could quickly respond to discoveries made from the ground, despite the need to schedule HST time long in advance. Working together, the SCP and the Space Telescope Science Institute implemented the strategy to superb effect.

The current study, based on HST observations of 11 supernovae, points the way to the next generation of supernova research: in the future, the SuperNova/Acceleration Probe, or SNAP satellite, will discover thousands of Type Ia supernovae and measure their spectra and their light curves from the earliest moments, through maximum brightness, until their light has died away.

SCP’s Perlmutter is now leading an international group of collaborators based at Berkeley Lab who are developing SNAP with the support of the U.S. Department of Energy’s Office of Science. It may be that the best candidate for a correct theory of dark energy will be identified soon after SNAP begins operating. A world of new physics will open as a result.

“New constraints on omega-m, omega-lambda, and w from an independent set of eleven high-redshift supernovae observed with the HST,” by Robert A. Knop and 47 others (the Supernova Cosmology Project), will appear in the Astrophysical Journal and is currently available online at http://www.arxiv.org/abs/astro-ph/0309368.

Berkeley Lab is a U.S. Department of Energy national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California.

Original Source: Berkeley News Release

Image credit: ESA

Gamma ray bursts (or GRBs) are the most powerful known explosions in the Universe. Although astronomers aren’t exactly sure what causes them, they’re somehow linked to supernovae explosions – it could be the formation of a black hole after the supernova explodes. When a GRB goes off, it funnels a tremendous amount of energy into two lighthouse-like beams that would probably vaporize anything out to 200 light-years away. Fortunately there aren’t any stars in our galactic neighborhood that has the potential to explode as a supernova, so we’re probably safe from such an event, but astronomers will keep looking? just to be sure.

For a few seconds every day, Earth is bombarded by gamma rays created by cataclysmic explosions in distant galaxies. Such explosions, similar to supernovae, are known as ?gamma-ray bursts? or GRBs.

Astronomers using ESA?s X-ray observatory, XMM-Newton, are trying to understand the cause of these extraordinary explosions from the X-rays given out for a day or two after the initial burst.

Danger to life?
However, the violence of the process begs the question, what happens to the space surrounding a GRB? A few years ago, some astronomers thought that a GRB might wipe out all life in its host galaxy.

That now seems to be a pessimistic view because the latest evidence shows that GRBs focus their energy along two narrow beams, like a lighthouse might do on Earth, rather than exploding in all directions like a bomb.

That does not mean that GRBs are not dangerous. Some theories suggest that anything caught in the beam, out to a distance of around 200 light years, will be vaporised.

Have there been GRBs in our own galaxy?
Although none of the recently detected GRBs seem powerful enough, events in the distant past are another question. ?There are a lot of supernova remnants in our galaxy, so I suspect that most probably there have been several GRBs as well,? says ESA astronomer Norbert Schartel.

While astronomers have yet to detect a really close GRB, they may already have picked up the most distant ones. ESA?s gamma-ray observatory, Integral, continues to collect invaluable data about GRBs on a daily basis, but last year XMM-Newton recorded the fading afterglow of X-rays that accompanied one GRB.

When Schartel and collaborators analysed the results, they found that the X-rays contained the ?fingerprints? of gas that was glowing like the X-ray equivalent of a ?neon? strip light.

Link between GRBs and exploding stars
This was the first piece of hard evidence that GRBs were linked to exploding stars, similar to supernovae. Now, XMM-Newton has captured another X-ray afterglow that shows similar features, strengthening the link.

Using these data and the discovery of visible explosions of some GRBs by NASA/ESA?s Hubble Space Telescope, astronomers have pieced together a picture of what happens.

It seems that the explosion of the star is just the first stage. The GRB itself is generated sometime later but whether that is hours, days or even weeks afterwards, no one yet knows. The GRB occurs when the centre of the exploding star turns into a ?black hole? and the X-rays are released as the GRB shock wave collides with the gas thrown off in the star?s original explosion.

Are we at risk from GRBs?
Another question still remains: could we be vaporised by a nearby GRB? The answer is no, even though there are GRBs detected almost everyday, scattered randomly throughout the Universe, it is highly unlikely. There are no stars within 200 light years of our Solar System that are of the type destined to explode as a GRB, so we do not expect to witness such an event at close range!

However, we do know that ESA?s scientific study of these fascinating ? and frightening ? cosmic events will continue for many years to come.

Original Source: ESA News Release