Tag: gamma ray bursts

More surprises from the Wolf-Rayet star numbered 104 and known for its pinwheel structure

2:03 pm

Keck infrared data of WR104

Among astronomers who study such things, Wolf-Rayet 104 is one of the most well known OB massive stars in their catalog, with the infrared picture to the right illustrating why. The star is actually a binary of massive stars, orbiting each other every eight months. Both produce strong winds, and the collision of those winds results in a glorious pinwheel structure that glows in the infrared.

Such stars are also believed to be major candidates to go supernova and in doing so produce a powerful gamma ray burst (GRB) that would shoot out from the star’s poles. As the orientation of this pinwheel suggests we are looking down into the pole of the system, this star system was actually considered a potentially minor threat to Earth. Located about 8,400 light years away, this is far enough away to mitigate the power of the GRB, but not eliminate entirely its ability to damage the Earth’s atmosphere.

New research now suggests however that despite the orientation of the pinwheel, face-on, the plane of the binary star system is actually tilted 30 to 40 degrees to our line of sight. The press release asks the new questions these results raise:

While a relief for those worried about a nearby GRB pointed right at us, this represents a real curveball. How can the dust spiral and the orbit be tilted so much to each other? Are there more physics that needs to be considered when modelling the formation of the dust plume?

You can read the paper here. It is a quite refreshing read, not just because of its relatively plain language lacking jargon, but because of its willingness to list at great length the uncertainties of the data.

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New gamma ray burst violates the explanations of scientists

9:04 am

The uncertainty of science: A newly discovered long gamma ray burst (GRB) that appears to have been formed by the merger of two neutron stars has contradicted the long held views of scientists as to the origin of this particular type of GRB.

Prior to the discovery of this burst, astronomers mostly thought that there were just two ways to produce a GRB. The collapse of a massive star just before it explodes in a supernova could make a long gamma-ray burst, lasting more than two seconds. Or a pair of dense stellar corpses called neutron stars could collide, merge and form a new black hole, releasing a short gamma-ray burst of two seconds or less.

But there had been some outliers. A surprisingly short GRB in 2020 seemed to come from a massive star’s implosion (SN: 8/2/21). And some long-duration GRBs dating back to 2006 lacked a supernova after the fact, raising questions about their origins. “We always knew there was an overlap,” says astrophysicist Chryssa Kouveliotou of George Washington University in Washington, D.C., who wrote the 1993 paper that introduced the two GRB categories, but was not involved in the new work. “There were some outliers which we did not know how to interpret.”

There’s no such mystery about GRB 211211A: The burst lasted more than 50 seconds and was clearly accompanied by a kilonova, the characteristic glow of new elements being forged after a neutron star smashup.

Kouveliotou’s claim is not how I remember things back in 1990s. Then, the astronomers seemed certain that the two GRB classes were entirely separate, with no overlap, despite the large number of uncertainties.

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Scientists puzzle over possible connection between a fast radio burst and a gamma ray burst

9:31 am

The uncertainty of science: In trying to explain the relatively new mystery of fast radio bursts (FRB), of which only about 20 have been detected and of which very little is known, scientists are intrigued by a gamma ray burst (GRB) that apparently occurred at the same time and place of one FRB.

Seeing the FRB event in a different wavelength would normally help astronomers better understand the FRB The problem is that this particular GRB only makes the mystery of FRBs more baffling.

One puzzle is that the two signals portray different pictures of the underlying source, which seems to be as much as 10 billion light years (3.2 gigaparsecs) away. Whereas the radio burst lasted just a few milliseconds, the γ-ray signal lasted between two and six minutes, and it released much more energy in total than the radio burst. “We’ve pumped up the energy budget more than a billion times,” says study co-author Derek Fox, an astrophysicist at Penn State.

This has big implications for the FRB’s origin. One leading theory suggests that FRBs are flares from distant magnetars — neutron stars with enormous magnetic fields that could generate short, energetic blasts of energy, and do so repeatedly, as at least one FRB is known to do. Although magnetars are thought to produce γ-rays, they would not emit such high energy and over such a long time, says Fox. “This is a severe challenge for magnetar models,” he says.

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A developing new astronomical mystery

8:58 am

Radio astronomers in Australia have recently detected a number of new mysterious radio bursts, dubbed fast radio bursts because of their nature, coming from outside our galaxy whose cause presently has no clear explanation.

An unprecedented double burst recently showed up along with four more of these flashes, researchers report online November 25 at arXiv.org.

Fast radio bursts, first detected in 2007, are bright blasts of radio energy that last for just a few milliseconds and are never seen again. Until now, astronomers had cataloged nine bursts that appeared to originate well outside the Milky Way. Yet, follow-up searches with nonradio telescopes for anything that might be pulsing or exploding keep coming up empty.

This mystery is similar to that of gamma ray bursts (GRBs), which were first discovered in the 1960s. About once a day there would be a short burst of gamma ray energy coming from scattered random directions in the sky, but no other radiation in any other wavelength. For decades astronomers didn’t know if the GRBs were coming from just outside our atmosphere or from billions of light years away. Finally, in the 1990s they pinned their location to the deaths of stars in distant other galaxies. As noted by one scientist at a conference, “GRBs signal the daily formation of a new black hole.”

Fast radio bursts are more intriguing. Because of their wavelengths and random locations on the sky, astronomers seem confident that they are occurring outside the Milky Way. However, in the eight years since their discovery only a handful have been detected, making it extremely difficult to study them. Nonetheless, they are significant because they signal some cataclysmic event far away, likely the death of a star in a way not yet understood or predicted. Finding out what that event is will produce important information about the evolution of our universe.

It just might take decades for this new mystery to be solved. Stay tuned!

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Astronomers have found evidence which suggests that most of the universe’s gold was created during the collision and merger of two neutron stars.

8:54 am

Astronomers have found evidence which suggests that most of the universe’s gold was created during the collision and merger of two neutron stars.

A binary of two neutron stars will eventually spiral into each other. When they do, scientists believe that their violent merger produces short gamma ray bursts (GRB). Observations of a short GRB burst in June found a lot of spectroscopic evidence of gold.

[T]he explosion had been responsible for the creation of a whole menagerie of heavy elements. They estimated that an equivalent of 1% of the sun’s matter was being flung out from the collision in a tail, and about 10 parts per million of that tail was made of gold.

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Last Saturday the space telescope Swift detected the most powerful gamma ray bursts ever detected.

7:59 pm

Last Saturday the space telescope Swift detected the most powerful gamma ray burst ever detected.

You can see the raw reports of the detection, followed up immediately by a host of other ground-based and space-based observations at this website. Click on the circulars for GRB130427A, starting with circular 14448. When this happened last Saturday I was out camping. When I got home there were dozens of circulars to look at. Based on the data here, this gamma-ray burst was relatively close for a grb, approximately 3.6 billion light years away.

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New data from a neutrino telescope in Antarctica had found that cosmic rays don’t come from gamma ray bursts, as had been believed by astronomers.

9:43 pm

The uncertainty of science: New data from a neutrino telescope in Antarctica has found that cosmic rays don’t come from gamma ray bursts, as had been believed by astronomers. You can read the paper here. [pdf]

Which means that astronomers at this moment have no idea what produces these high energy cosmic rays.

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