Podcaster: Richard Drumm
Title: Space Scoop: Relics of the Early Universe are Dustier Than Expected
Organization: Astrosphere New Media
Link : astrosphere.org ; http://unawe.org/kids/unawe1423/
The original press release: http://www.eso.org/public/news/eso1418/
Description: Space scoop, news for children.
Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.
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Transcript:
This is 365 Days of Astronomy. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.
Today’s story is…
Relics of the Early Universe are Dustier Than Expected
The ALMA radio telescope array in Chile’s Atacama desert has been delving through the dusty corners of the Universe to uncover the secrets of the biggest explosions ever!
Gamma-Ray Bursts (or GRBs) are the brightest explosions in the Universe. They release more energy in 10 seconds than the Sun will in its entire 10 billion year lifetime! Yeah. Billion.
We only see GRBs in very distant galaxies; galaxies so far away that it takes billions of years for their light to reach us. This means that when we look at these galaxies through telescopes, we are seeing them as they were billions of years ago, when the Universe was still young. The Universe is 13.8 billion years old, by the way, in case you didn’t know…
Astronomers think that GRBs are caused by the detonation of massive stars at the end of their lives. These blazing bursts of light are normally followed by a fainter afterglow, which is thought to be created by collisions between the ejected material from the explosion and the surrounding gas that was there before the explosion.
However, some gamma-ray bursts mysteriously seem to have no afterglow. These are referred to as “dark bursts” or dark GRBs.
One explanation for these dark bursts is that the explosion is hidden by clouds of cosmic dust, which block the faint light. Cosmic dust, just so you know, is different from the dust under my bed, and is made of tiny bits of matter thrown off by supernova explosions. Bits of carbon, iron, you name it, the whole periodic table of the elements. However, this challenges another belief that GRBs should be surrounded by large amounts of gas– the gas from which the original stars were made. The 2 main gasses here are hydrogen & helium.
Until now, we haven’t had telescopes powerful enough to peer into the distant Universe to solve this cosmic conundrum. But ALMA came to the rescue.
Using that giant telescope array, astronomers have been studying two galaxies that GRBs were recently spotted in. In a complete surprise, less gas was observed than was expected, and correspondingly much more dust than was expected too, making some GRBs appear as “dark GRBs”.
Another remarkable achievement made possible by the high resolution of ALMA was uncovering the distribution of molecular gas and dust in GRB host galaxies. Observations of the GRB 020 819B revealed a remarkably dust-rich environment in the outskirts of the host galaxy, whereas molecular gas was found only around its centre. This is the first time that such a distribution among GRB host galaxies has been seen.
Here’s a quote from Dr. Bunyo Hatsukade from the National Astronomical Observatory of Japan, the NAOJ:
“We didn’t expect that GRBs would occur in such a dusty environment with a low ratio of molecular gas to dust. This indicates that the GRB occurred in an environment quite different from a typical star-forming region,”
This suggests that massive stars that die as GRBs, change the environment in their star-forming region before they explode.
The research team believes that a possible explanation for the high proportion of dust compared to molecular gas at the GRB site is the difference in their reaction to ultraviolet radiation.
Since the bonds between atoms which make up molecules are easily broken by ultraviolet radiation, molecular gas cannot survive in an environment exposed to the strong ultraviolet radiation produced by the hot, massive stars in its star-forming region, including the one that would eventually explode as the observed GRB.
Although a similar distribution is also seen in the case of GRB 051 022, this has yet to be confirmed due to the lack of resolution (as this GRB host galaxy is located farther away than the GRB 020 819B host galaxy).
ALMA has a resolution that is changed by spreading the antennas farther apart, so this higher resolution will be easy to obtain soon.
There is a trade-off, though, as the widely spread high resolution antenna placement doesn’t have high sensitivity at the same time. You have a choice with it: High sensitivity with lower resolution or low sensitivity with a high resolution.
There is a section of the array formerly called the ACA, the Atacama Compact Array that is a tight cluster of sensitive antenna dishes that can help here. It’s rather like having a wide angle lens embedded in a telephoto lens. So you can to some extent have the best of both worlds!
In any case, these ALMA observations support the hypothesis that it is dust that absorbs the afterglow radiation, causing the dark gamma-ray bursts.
Thank you for listening to 365 Days of Astronomy!
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