Most Violent Event in Universe Observed -Exploding Super-Massive Star

ESA-GRB-impression
In this new image from the Hubble Space Telescope, you'll see a spectacular gamma ray burst and supernova as a bright point in the irregular galaxy located approximately 820 million light years from the Earth. An international team of researchers made the discovery using NASA's Swift satellite.


"That we have observed a gamma ray burst and a supernova simultaneously is unusual and it gives us a long awaited confirmation of the theory that gamma ray bursts are indeed associated with exploding giant stars", explains Johan Fynbo, astrophysicist at the Dark Cosmology Center, Niels Bohr Institute at the University of Copenhagen.

They then observed the phenomenon from the European Very Large Telescopes, VLT in Chile, where using the special X-shooter instrument they could observe the object's light spectrum all the way from the ultraviolet to near the infrared at the same time.

By analyzing the light spectra and measuring the so-called redshift the researchers could calculate the distance to the supernova, which was located in a galaxy 820 million light years from the Earth. It sounds extremely far away, but for astronomers it is a relatively near galaxy and that is a true delight.

"Only about one out of 10,000 supernovae produce gamma ray bursts, and gamma ray bursts in the relatively near universe are even more rare, so it gives us a unique opportunity to study the phenomena in detail. When you have one that is so near, it is like a clock telling you that the star is dying just NOW, and you can follow the early phases and the entire development of the supernova explosion that follows", explained Johan Fynbo.

It is only the very large, massive stars of more than 30-40 solar masses that produce gamma ray bursts. What happens is that when the star dies, it collapses and forms a black hole. If the black hole spins very quickly, a jet might appear – a gamma ray burst, which is powerful, high-energy radiation, which shoots out at nearly the speed of light. It happens very quickly and only lasts a few seconds.

The actual star explosion, the supernova, happens instantaneously, but it evolves and becomes brighter and brighter over the next 10 – 14 days, after which it gradually becomes weaker again over the course of several months.

The spectra show that it was a metal-poor star that exploded. It only had around half the amount of heavy elements as the Sun – our star. This means that it was an early development of stars. The galaxy the star was located in was irregular and it is typically in such galaxies, that you find metal-poor massive stars in the local universe.

"It is fantastic that we can now study exploding giant stars and the related gamma ray bursts in detail – we have only been able to do this 3-4 times before", explains Johan Fynbo.

The image below is an enlargement of a combined image obtained with the Space Telescope Imaging Spectrograph (STIS) onboard the NASA/ESA Hubble Space Telescope through a clear filter (shown in blue) and a red filter (shown in red). The region shows the star-formation taking place around the gamma-ray burst region in the galaxy ESO 184-G82.

At the exact position of the gamma-ray burst (marked with lines on the lower right image) a very compact source of emission is seen. Most of this emission is probably the last remnant of the fading light from the supernova itself, but the scientists suspect that a faint underlying star cluster may contribute as well.

Image Credit: ESA, Stephen Holland (Danish Centre for Astrophysics with the HST), Jens Hjorth, Johan Fynbo (University of Copenhagen)

The Daily Galaxy via University of Copenhagen

 

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