A really, really long time ago in a galaxy far away, a massive star exploded. On April 23, 2009, the Swift satellite detected that explosion. This spectacular gamma ray burst was seen 13 billion light years away, with a redshift of 8.2, the highest ever measured. As we hinted yesterday, this object is now the most distant known object, and the burst occurred when the Universe was only 630 million years old, a mere one-twentieth of its current age. This event, called GRB 090423, can tell us much about the early Universe. “We completely smashed the record with this one,” said Edo Berger, a professor at Harvard University and a member of the team that first measured the burst’s origin. “This demonstrates for the first time that massive stars existed in the early Universe.”
At 3:55 a.m. EDT on April 23, Swift detected a ten-second-long gamma-ray burst of modest brightness, and quickly slewed around to use its Ultraviolet/Optical and X-Ray telescopes on the burst location. Swift saw a fading X-ray afterglow but nothing in visible light. A number of ground based telescopes were alerted to the event and within three hours began to observe the distant GRB.
“This was a pretty amazing event,” Berger told Universe Today. “Swift detected this gamma ray burst on April 23 and we immediately followed it up with the Gemini North Telescope in Hawaii, after it was demonstrated it did not have a visible light counterpart. That was the initial hint that this might be a distant object. We observed it in infrared and we found in the different infrared bands that there was a sharp break at a wavelength of about 1.1 microns.”
The drop-out corresponds to a redshift of 8.2 and burst distance of about 13 billion light-years.
Other telescopes that made observations were the Very Large Telescope, STFC’s United Kingdom Infrared Telescope (UKIRT), The Telescopio Nazionale Galileo (TNG), the Okayama Astrophysical Observatory, the Fermi Space Telescope and the Plateau de Bure Interferometer.
Subsequent observations the following night from other telescopes confirmed and refined the measurement. Previously, the most distant known object was a galaxy with a redshift of 6.96 discovered in 2006. The most distant GRB found September of 2008 had a redshift of 6.7. “We completely smashed the record with this one,”said Berger. “I think people were thinking it would happen step by step, but we kind of jumped things.”
Berger said the burst itself was not unusual; it was a basic a run-of-the–mill GRB. But even that can convey a lot of information. “That might mean that even these early generations of stars are very similar to stars in the local universe, that when they die they seem to produce similar types of gamma ray bursts, but it might be a little early to speculate.”
So what does this distant GRB tell us about the early Universe? “This happened a little more than 13 billion years ago,” said Berger. “We’ve essentially been able to find gamma ray bursts throughout the Universe. The nearest ones are only about 100 million light years away, and this most distant one is 13 billion light years away, so it seems that they populate the entire universe. This most distant one demonstrates for the first time that massive stars exist at those very high red shifts. This is something people have suspected for a long time, but there was no direct observational proof. So that is one of the cool results from this observation.”
Berger said this event also tells us that perhaps GRBs are the best objects to study which show how the early Universe evolved. “They are extremely bright and very easy to find, comparatively speaking, so they give us hope that this is the right approach. Over the years people have found high redshift quasars and galaxies, but my suspicion is that until the launch of the James Webb Space Telescope the middle of the next decade, this object will remain as the record holder. No other telescope, including the Hubble Space Telescope is capable of finding more distant objects.”
Finding this distant object also demonstrates how telescopes around the world can work together. “It’s the combination of Swift pinpointing where these objects are located and the ground-based telescopes immediately responding to these positions and then demonstrating the distance,” said Berger. “It’s really a great synergy. We’ve been doing this for a long time now, and I think part of what has been driving this is the desire to find such distant objects.
Berger said astronomers have been speculating about such distant gamma rays bursts for quite some time and there are two missions being proposed to NASA as the next generation gamma ray telescopes. So, now, the fact that we’ve now found one at such a high distance makes those satellites more attractive for funding because this has now gone from being an idea or gut feeling to real observational proof.”
Source: Interview with Edo Berger