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Posted on Oct. 16, 2018
On October 16, 2017, an international group of astronomers and physicists enthusiastically announced the first simultaneous detection of light and gravitational waves from the same source: a fusion of two neutron stars. Now a team including several astronomers from the University of Maryland has identified a direct relative of this historic event.
The newly described object, named GRB150101B, was reported as a gamma surge located by NASA's Neil Gehrels Swift observatory in 2015. Follow-up observations by NASA's Chandra X-ray observatory , the Hubble Space Telescope (HST) and the Discovery Channel Telescope (DCT) suggest that GRB150101B shares remarkable similarities with the fusion of neutron stars, named GW170817, discovered by the LIGO (Laser Interferometer) Gravitational Wave Observatory and observed by multiple photophase telescopes in 2017.
A new study suggests that these two distinct objects may, in fact, be directly related. The results were published on October 16, 2018 in Nature Communications.
"It's a big step forward to move from one detected object to two," said the study's lead author, Eleonora Troja, an associate researcher at UMD's Department of Astronomy, in conjunction with Goddard Space Flight Center of NASA. "Our discovery tells us that events such as GW170817 and GRB150101B could represent a whole new category of erupting objects that can be turned on or off, and that might actually be relatively common."
Troja and his colleagues suspect that both GRB150101B and GW170817 were produced by the same type of event: a fusion of two neutron stars. These catastrophic coalesces each generated a narrow jet, or beam, of high energy particles. The jets each produced a short, intense burst of gamma rays (GRB), a powerful flash lasting only a few seconds. GW170817 also created space-time waves, called gravitational waves, suggesting that this could be a common feature of neutron star fusions.
The apparent correspondence between GRB150101B and GW170817 is striking: the two produced an exceptionally weak and short burst, and both were a bright, blue optical light source and long-lasting X-ray emission. Host galaxies are also remarkably similar, based on HST and DCT observations. Both are bright elliptical galaxies with a population of stars a few billion years old that show no evidence of new star formation.
"We have a case of cosmic look-alikes," said Geoffrey Ryan, co-author of the study, postdoctoral researcher at UMD's Department of Astronomy and a member of the Joint Space-Science Institute. "They look alike, act the same way and come from similar neighborhoods. The simplest explanation is that they belong to the same family of objects. "
In GRB150101B and GW170817, the explosion was probably "out of line", ie the jet did not point directly to the Earth. Until now, these events are the only two short off-axis GRBs identified by astronomers.
The optical emission of GRB150101B is largely in the blue part of the spectrum, which provides an important clue that this event is an extra kilonova, as shown in document GW170817. A kilonova is a flash of radioactive light producing large quantities of important elements like silver, gold, platinum and uranium.
Although there are many commonalities between GRB150101B and GW170817, there are two very important differences. One of them is their location: GW170817 is relatively close, about 130 million light years from Earth, while GRB150101B is about 1.7 billion light years away. .
The second important difference is that, unlike GW170817, there is no gravitational wave data for GRB150101B. Without this information, the team can not calculate the masses of the two objects that have merged. It is possible that the event results from the fusion of a black hole and a neutron star, rather than two neutron stars.
"It's probably only a matter of time before another event like GW170817 provides both gravitational wave data and electromagnetic images. If the next observation of this type reveals a fusion between a neutron star and a black hole, it would be truly revolutionary, "said co-author of the study, Alexander Kutyrev, associate researcher at the Department of Energy. UMD astronomy with a joint appointment at Goddard Space NASA Flight Center. "Our last observations give us hope that we will see such an event for too long."
It is possible that some mergers, such as those observed in GW170817 and GRB150101B, have already been detected, but have not been correctly identified using complementary observations in different wavelengths of light, according to Researchers. In the absence of such detections, particularly at longer wavelengths such as X-rays or optical light, it is very difficult to determine the precise location of events that produce bursts. gamma.
In the case of GRB150101B, astronomers first thought that the event could coincide with an X-ray source detected by Swift in the center of the galaxy. The most likely explanation of such a source would be a supermassive black hole devouring gas and dust. However, later observations with Chandra have placed the event further away from the center of the host galaxy.
According to the researchers, even if LIGO had been operational in early 2015, it would most likely not have detected gravitational waves from GRB150101B because of the greater distance between the event and the Earth. Nevertheless, each new event observed with LIGO and multiple light gathering telescopes will add important new pieces to the puzzle.
"Each new observation helps us better identify the kilonovae with the help of fingerprints: money creates a blue color, while gold and platinum add a hint of red, for example, "added Troja. "We were able to identify this kilonova without gravitational wave data, so maybe in the future we can even do it without directly observing a gamma surge."
Image at the top of the page: Illustration of an artist illustrating the fusion of two neutron stars. University of Warwick / Mark Garlick
The Daily Galaxy via NASA and the University of Maryland
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