Radio frequency wavelengths in the millimeter range have been captured for the first time since an epic collision involving at least one neutron star.
The result is a recording of a short duration gamma-ray burst—one of the most energetic ever observed, and one of the brightest dull afterglows we’ve ever seen. The data can help scientists learn more about these extreme events and their impact on the space around them.
And there is an incredible timeliness of the event, whose light has traveled about 6 to 9 billion light-years across the universe, to be picked up by the Atacama Large Millimeter/submillimeter Array (ALMA) in November 2021.
“This small gamma-ray burst was the first time we’ve tried to observe such an event with ALMA,” said Northwestern University physicist Wen-Fi Fong.
“The afterglow is very difficult for short bursts to come by, so it was fantastic to capture this event shining so brightly. After many years of observing these bursts, this surprising discovery opens up a new area of study, as it allows us to see many more.” Inspires to observe more of these in the future with ALMA, and other telescope arrays.”
Gamma radiation bursts are the most powerful known explosions in the universe. In just 10 seconds, a gamma-ray burst can emit more energy than a star like the Sun gives out in 10 billion years.
And they are important; As we saw in earlier neutron star collisions, it is in such explosions that elements heavier than iron are forged and released into the universe. The gold ring you’re wearing on your finger is the product of a highly stellar disaster.
We know that neutron star collisions produce a type of gamma-ray burst known as a short-period gamma-ray burst, or SGRB. These last only milliseconds, and leave behind a bright afterglow as the ejecta collides with the explosion and interacts with the gas of the interstellar medium.
Typically, these SGRBs are not observed at radio wavelengths, which can make them a bit difficult to interpret.
“These explosions occur in distant galaxies, which means that the light from them may be too low for our telescopes on Earth,” explained astrophysicist Tanmay Lasker of Radboud University in the Netherlands.
“Prior to ALMA, millimeter telescopes were not sensitive enough to detect these afterglows.”
Because this particular event, named GRB 211106A, was so distant, it could not be detected by our current gravitational wave astronomy instruments. The energetic X-rays accompanying the brief explosion were picked up by NASA’s Neil Gehrels Swift Observatory.
However, galaxies as distant as GRB 211106A’s host are not detectable at X-ray wavelengths – and the dust in this region meant Hubble’s optical observations were no better at pinpointing the source.
For that reason, only scientists working with X-ray bursts thought that the location of the explosion was relatively close. So he turned to ALMA, the first time millimeter-wavelength had been used to observe and refer to the phenomenon of gamma-ray bursts.
“Hubble observations revealed an irreversible region of galaxies,” Lasker said.
“The unique sensitivity of ALMA allowed us to pinpoint the location of the GRB in that region with much greater precision, and it turned out to be in another faint galaxy, which is further away.
“This, in turn, means that this short-duration gamma-ray burst is even more powerful than we previously thought, making it one of the brightest and most energetic on record.”
When neutron stars collide, the result is spectacular: an explosion with jets of material that eject at a significant percentage of the speed of light. If we’re lucky, those jets are oriented in such a way that one is more or less directed toward us, so that we see the explosion as a gamma-ray burst.
Millimeter-wavelength observations allowed the researchers to measure some key properties of GRB 211106a; Namely, the opening angle of the jet, which can be used to estimate the rates of SGRBs in the universe, and a more accurate measurement of the GRB’s energy.
“Millimetre wavelengths can tell us about the density of the atmosphere around GRBs,” said Northwestern University astronomer Genevieve Schroeder.
“And, when combined with X-rays, they can tell us about the actual energy of the explosion. Because emission at millimeter wavelengths can be detected for a longer period of time than X-rays, millimeter emission can also be detected.” can be used to determine the width of the GRB jet.”
The researchers found that GRB 211106a has some unusual properties, both in its host galaxy and in its energetic profile.
This ultimately suggests that the properties of SGRBs are more diverse than they currently are, meaning that continued observation and classification of these phenomena is warranted.
So, while this may be the first millimeter of penetration in these incredible explosions, it is unlikely to be the last.
“ALMA breaks down the playing field in terms of its capabilities at millimeter wavelengths and enables us to see the faint, dynamic universe in this type of light for the first time,” Fong said.
“After a decade of observing tiny GRBs, it’s really amazing to see the power of using these new technologies to uncover the amazing gifts from the universe.”
research has been accepted The Astrophysical Journal Lettersand is available on arXiv.