Strange new bursts of gamma rays point to a new way to destroy a star

Apr 16, 2013
An artist's impression of the stars creating gamma-ray bursts. The background blue star is the progenitor of a standard long duration gamma-ray burst. A so-called Wolf-Rayet star, it has a mass ten or more times the mass of the sun but has a comparable size. The foreground star is the suggested progenitor of an ultra-long gamma-ray burst (GRB). It has a mass of perhaps 20 times the sun but is up to a thousand times larger. In both cases the GRB is produced by a jet punching through the star, but in the case of the ultra-long GRBs the much larger size of the star creates a much longer lived jet. Image copyright Mark A. Garlick, used with permission by the University of Warwick

(Phys.org) —A team led by the University of Warwick has pinpointed a new type of exceptionally powerful and long-lived cosmic explosion, prompting a theory that they arise in the violent death throes of a supergiant star.

These explosions create powerful blasts of high energy gamma-rays, known as gamma-ray bursts, but while most bursts are over in about a minute, this new type can last for several hours.

The first example was found by astronomers on Christmas Day 2010, but it lacked a measurement of distance and so remained shrouded in mystery with two competing theories put forward for its origin.

The first model suggested it was down to an asteroid, shredded by the gravity of a dense neutron star in our own galaxy, the second that it was a supernova in a galaxy 3.5 billion light years away, or in the more common language of astronomers at a redshift of 0.33.

A new study by a team of scientists led by Dr Andrew Levan at the University of Warwick finds several more examples of these unusual and shows that the Christmas Day burst took place in a galaxy much further away than the two theories suggested.

This research is to be presented at the GRB 2013 Symposium in Nashville, Tennessee on Tuesday 16 April.

Using data from the in Hawaii, the scientists calculated that this ultra-long gamma-ray burst had a redshift of 0.847. This gives it a location of approximately half-way to the edge of the , or 7 billion light years away.

Armed with its location, Dr Levan's team, which included scientists from an international collaboration, has developed a new theory to explain how it occurred.

The durations of gamma-ray bursts and the inferred sizes of their progenitors. The lower panel shows the three types of GRB, the short and long duration bursts that have been known for many years and the newly discovered population of ultra-long GRBs. Credit: Andrew Levan, University of Warwick

They suggest this kind of burst is caused by a supergiant, a star 20 times more massive than the sun, which evolves to become among the biggest and brightest stars in the universe with a radius of up to 1 billion miles - up to 1,000 times that of the sun.

They believe the ultra-long durations of the Christmas gamma-ray burst and two other similar bursts are simply down to the sheer size of the supergiants exploding in a supernova.

Most stars that create gamma-ray bursts are thought to be relatively small and dense, and the explosion that destroys them punches through the star in a matter of seconds. In the case of these new ultra-long bursts the explosion takes much longer to propagate through the star, and so the gamma-ray burst lasts for a much longer time..

Dr Levan said: "These events are amongst the biggest explosions in nature, yet we're only just beginning to find them.

"It really shows us that the Universe is a much more violent and varied place than we'd imagined.

"Previously we've found lots of gamma-ray events with short durations, but in the past couple of years we've started to see the full picture."

Nial Tanvir, a professor at the University of Leicester, and second author of the study added: "We believe that powering the explosion is a newly formed black hole in the heart of the star.

"Predicting the detailed behaviour of matter falling into a black hole in these circumstances turns out to be very difficult, and from a theoretical point of view we didn't initially expect explosions at all.

"The amazing thing is that nature seems to have found ways of blowing up a wide range of in the most dramatic and violent way."

The more common type of gamma-ray burst is thought to be caused when a Wolf-Rayet star in the final phase of its evolution collapses into a black hole at its own core.

Matter is drawn into the black hole, but some of its energy escapes and is focussed into a jet of material which blasts out in two directions forming copious gamma-rays in the process.

These jets are ejected extremely quickly (close to the speed of light), otherwise the material would fall into the black hole from which it can't escape. For this reason they last only a few seconds.

However, a gamma-ray burst in a bigger star the size of a supergiant needs to power through a larger reservoir of material, hence its longer duration.

Explore further: Thermonuclear X-ray bursts on neutron stars set speed record

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Q-Star
2 / 5 (4) Apr 16, 2013
I'm not sure the article missed this, but another reason for the longer apparent duration is the difference in the distance/travel time from one side of the event to the other and how the edges of the event are oriented to us.

Did I miss that in the article? Anyhoo, it will be some interesting stuff to follow as the telescopes keep getting bigger and better.
JohnMoser
not rated yet Apr 16, 2013
Though the explosion may have occurred around 7 billion years ago, the actual distance would be around 23 billion light years.
Lurker2358
1 / 5 (3) Apr 16, 2013
I laugh at the error in the red shift calculation: 0.33 vs 0.847.
Q-Star
3.5 / 5 (8) Apr 16, 2013
I laugh at the error in the red shift calculation: 0.33 vs 0.847.


And I'm sure they are laughing at ya. To think that the VERY FIRST observation of a NEW phenomena would yield spot on accurate results,,,,,

I'm also thinking they might be laughing at ya for finding it laughable that after three years and more objects observed that new and improved findings might differ from the FIRST one seen.
StarGazer2011
4 / 5 (8) Apr 16, 2013
So even with redshift 0.847 the rays are still in the gamma range, imagine how short the wavelength must have been where/when they were emitted!
g_g_kanev
not rated yet Apr 17, 2013
Interestigly!
GSwift7
5 / 5 (1) Apr 17, 2013
I laugh at the error in the red shift calculation: 0.33 vs 0.847


the 0.33 number wasn't an observation. That was a theory proposed to explain an observation without a distance measurement. The 0.847 number came from another observation which included a distance measurement, essentially proving the previous theory to be wrong. Since that was one of two pre-existing theories, as mentioned in the article, it turns out that BOTH of the previous theories had been wrong.

So even with redshift 0.847 the rays are still in the gamma range


What we call gamma rays covers a rather large piece of spectrum, and the amount the frequency changes in response to a given z number of redshift is proportional to its original frequency. Short wavelengths are not stretched as much as long wavelengths at the same level of Z.
GSwift7
1 / 5 (1) Apr 17, 2013
Though the explosion may have occurred around 7 billion years ago, the actual distance would be around 23 billion light years


There's that same stupid idea that some of us were fighting about in another thread a couple of weeks ago.

We haven't moved away from this object faster than light speed. If we had, you wouldn't see it at all.

In fact, you're implying that we've been moving away from this thing at more than twice the speed of light. From 7 billion LY to 23 billion LY in only 7 billion years? Haha, think about that one again. lol, that would be 16 billion LY in 7 billion years.
Mumrah
5 / 5 (3) Apr 17, 2013

We haven't moved away from this object faster than light speed. If we had, you wouldn't see it at all.

That's irrelevant as space itself is what's expanding. I've not done the maths but the principle sounds reasonable based on this:-

http://www.astro.....html#DN
Q-Star
2.8 / 5 (6) Apr 17, 2013

We haven't moved away from this object faster than light speed. If we had, you wouldn't see it at all.

That's irrelevant as space itself is what's expanding. I've not done the maths but the principle sounds reasonable based on this:-

http://www.astro.....html#DN


Ya are entirely correct. There is no constraint in physics as we know them for the space to able to expand at a rate faster than light speed. Many very conventional models predict it taking place during various eras in the cosmological history of the universe.
GSwift7
1 / 5 (1) Apr 17, 2013
If you were to leave today at the speed of light and travel to this place, it would take you 7 billion LY to get there. When you talk about equivelant increase in distance, it's not a literal increase in distance. Space itself expanded. It didn't add space between us and them.
Q-Star
2 / 5 (4) Apr 17, 2013
If you were to leave today at the speed of light and travel to this place, it would take you 7 billion LY to get there. When you talk about equivelant increase in distance, it's not a literal increase in distance. Space itself expanded. It didn't add space between us and them.


But that is exactly what we observe, added space. It would take 7 Gly to get to "where it was" 7 Gly ago.

That is the entire foundation of the Concordance Model of cosmology. The space is expanding but not the matter that occupies that space. GR predicts it. Hubble observed it. All the science done since Hubble, and LeMaitre has only confirmed it. The science that the CMB is based on. Space expands, matter does not. The distances between objects increases without constraint by the laws of physics as applied to matter.

Fleetfoot
1 / 5 (1) Apr 20, 2013
When you talk about equivelant increase in distance, it's not a literal increase in distance. Space itself expanded. It didn't add space between us and them.


Q-Star and Mumrah are right, literal expansion of distances between widely separated objects is the Big Bang model.

There's that same stupid idea that some of us were fighting about in another thread a couple of weeks ago.


This is the article:

http://phys.org/n...axy.html

We haven't moved away from this object faster than light speed. If we had, you wouldn't see it at all.


A few posts down in that thread, I outlined a toy model. As I suggested, if you increase the expansion to 10% per step, it will illustrate light reaching us from a source which was receding by more than one light year per year.

The bottom line is that you can't judge cosmology using SR because it is only valid in the absence of gravity.