24Oct2012

Brilliant Quasar Blanketed By Dust?

This artist's impression of one of the most distant, oldest, brightest quasars ever seen is hidden behind dust. The quasar dates back to less than one billion years after the big bang. The dust is also hiding the view of the underlying galaxy of stars that the quasar is presumably embedded in. (Credit: NASA/ESA/G.Bacon, STScI)

The Hubble Space Telescope has been busy again… Busy looking at one of the brightest and most distant quasars in the Universe.We sure are looking far back into time here!

While that might not seem like news, what astronomers weren’t expecting was to find was the host galaxy doesn’t appear to be feeding its quasar. How can that be? Is it possible the galaxy is so full of dust that it’s hiding the stars? Can the James Webb Space telescope reveal what’s hidden?

As we know, all galaxies are home to dust. During the time of the early Universe, most of space was dust-free until the first generation of stars began coughing out dust through nuclear fusion. When these stars reached the end of their lifetimes, they filled this “empty space” with dust – the product of their loss of atmosphere. The quasar belongs to that time period, roughly a billion years after the Big Bang. Through sub-millimeter observations, it was known to be home to copious amounts of dust. However, astronomers weren’t quite prepared to learn just how well this dust is blocking starlight from inside the galaxy. Apparently no starlight seems to become from around the quasar itself.

The quasar is the brilliant core at the galactic center – the region where the “stuff” that fuels a super-massive black hole is falling inward. The black hole becomes so well fed that it releases intense jets of radiation – a light which can appear to be a quasar if aimed in Earth’s direction. This “light” can outshine the surrounding galaxy by as much as a thousand times. In the case of the Hubble observations, this particular black hole could be consuming as much mass as a few Suns per year and have taken on as many as three billion solar masses over the last few hundred million years.

“If you want to hide the stars with dust, you need to make lots of short-lived massive stars earlier on that lose their mass at the end of their lifetime. You need to do this very quickly, so supernovae and other stellar mass-loss channels can fill the environment with dust very quickly,” said Rogier Windhorst of Arizona State University (ASU), Tempe, Arizona. “You also have to be forming them throughout the galaxy to spread the dust throughout the galaxy,” added Matt Mechtley, also of ASU.

First spotted by the Sloan Digital Sky Survey (SDSS), this quasar belongs to only a small amount of its known distant companions. Through subsequent sub-millimeters observations, astronomers knew there was a huge amount of dust in the host galaxy, but they didn’t know exactly how it was distributed or even if star clusters might be visible. After, all, most galaxies, even the dusty ones, have some visible evidence of stars! By employing the Hubble, the researchers began their quest to remove light from the quasar image and search for stars. The team found a single star to use as a reference and began removing the quasar’s light from the image. With the quasar gone, they were astonished to find the starlight was also gone. The galaxy’s stars should have easily been disclosed if they were there and at least partially unobscured by dust. There had to be some stars somewhere! ( This result was published in the Sept. 10 issue of the Astrophysical Journal Letters in a paper by M. Mechtley, R. Windhorst, and an international team of collaborators. )

This is a Hubble Space Telescope view of one of the most distant and luminous quasars ever seen (circled in white) and dates to less than one billion years after the big bang. This near-infrared light image was taken with Hubble's Wide Field Camera 3 in December 2010 and January 2011. (Credit: NASA/ESA/M. Mechtley, R. Windhorst, Arizona State University)

“It is remarkable that Hubble didn’t find any of the underlying galaxy,” said Windhorst. “The underlying galaxy is everywhere, much fainter than expected.” That’s the tricky part.

It  therefore must be in a very dusty environment throughout. It’s one of the most rip-roaring forest fires in the universe. It’s creating so much smoke that you’re not seeing any starlight, anywhere. The forest fire is complete, not a tree is spared.”

“Because we don’t see the stars, we can rule out that the galaxy that hosts this quasar is a normal galaxy,” said Mechtley. “It’s among the dustiest galaxies in the universe, and the dust is so widely distributed that not even a single clump of stars is peeking through. We’re very close to a plausible detection, in the sense that if we had gone a factor of two deeper we might have detected some light from its young stars, even in such a dusty galaxy.”

Stars aren’t exactly a small object which can be easily hidden by dust. It’s just time to break out a different kind of “cleaning” equipment and NASA’s planned James Webb Space Telescope will peer beyond the veil. Its infrared sensitivty will allow it to look back as far as 200 million years after the Big Bang. If galaxies were forming stars at this early age, the Webb will reveal them.

“The Webb telescope is designed to make a definitive detection of this,” said Windhorst.” We will get solid detections of the stars with Webb’s better sensitivity to longer wavelengths of light, which will better probe the dusty regions in these young galaxies.”

Original Story Source: NASA James Webb Space Telescope News. Submitted by Tammy Plotner for “Dave Reneke’s World of Space and Astronomy News”.

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