Across the universe, 5.5 billion light years away, a number of telescopes have recorded a bright flash of a short gamma ray burst. Very similar to the explosion of a kilonova star.
Astronomers tried to link the data with a collision of neutron stars, which was recorded for the first time in history back in 2017.
The discovery of 2017, known as GW 170817, was a great boon: a huge amount of data on a variety of signals that help us understand events and recognize what we are looking at if a similar phenomenon reappears.
But there is something about the kilonova accompanying the gamma-ray burst, called GRB 200522A, very different from that collision of neutron stars. The flare, captured by the Hubble Space Telescope in the near infrared, was incredibly bright – 10 times brighter than neutron star collision models predicted.
“These observations do not fit with traditional explanations for short bursts of gamma rays,” said astronomer Wen-fi Fong of Northwestern University.
“Given what we know about radio and X-rays from this explosion, this is not a collision. The near-infrared radiation that we detect with Hubble is too bright. '
The radiation was first detected by NASA's Neil Gerels Swift Observatory, a space telescope designed to detect gamma-ray bursts. As soon as the warning was received, other space and terrestrial telescopes began to tune in to the explosion site.
A very large array, W.M. The Keck Observatory and the Las Cumbres Observatory's network of global telescopes worked to obtain an electromagnetic profile of an event from radio waves to X-rays. They showed that it was a short gamma-ray burst – a type of explosion lasting less than two seconds associated with the merger of neutron stars.
But the Hubble Space Telescope, which observes the phenomenon in the near infrared, has changed the mind of scientists.
“As the data came in, we formed a picture of the light-emitting mechanism that we saw,” said astronomer Tanmoy Laskar of the University of Bath in the UK.
“We had to completely change our thought process because the information that Hubble added made us realize that we must abandon traditional thinking and assume that a new phenomenon is happening. Then we had to figure out what these extremely powerful explosions mean for physics. '
The collision of two neutron stars – the collapsing cores of dead stars – is a landmark event. Neutron stars are tiny and dense, about 1.1 to 2.5 times the mass of the Sun, but packed into a sphere only 20 kilometers across.
When they collide, they release a tremendous amount of energy in the form of an explosion of a kilonova star 1,000 times brighter than a normal nova. This is accompanied by a burst of high-energy gamma rays from jets of ejected matter moving at a speed close to the speed of light.
The kilonova itself is a glow in the optical and infrared ranges of waves, caused by the radioactive decay of heavy elements. Astronomers believe that two neutron stars in GW 170817 have merged to form a black hole. The researchers believe that the near-infrared brightness of kilon GRB 200522A indicates that the two neutron stars have merged to form something else: a magnetar.
Magnetars are a type of neutron star, but they have insanely powerful magnetic fields – about 1000 times more powerful than the average neutron star.
Magnetars are very rare; only 24 have been discovered to date in the Milky Way. Because of this, it is rather difficult for us to understand how they arise. If two neutron stars associated with GRB 200522A formed a magnetar, this gives us a new mechanism through which these extreme stars could arise.
“We know magnetars exist because we see them in our galaxy,” Fong said.
“We think most of them are formed from explosions of massive stars, leaving highly magnetized neutron stars. However, it is possible that a small fraction of them are formed when neutron stars merge. We've never seen evidence of this before. '
To date, only one kilonova, GW 170817, has been confirmed and well characterized.
But the new study is a step towards cataloging the possible variety of kilon stars and understanding the range of results when two neutron stars collide.
The study is accepted for publication in The Astrophysical Journal and is available on arXiv.
Sources: Photo: (NASA, ESA, and D. Player / STScI)
