In the picture we can see a red dot. This red dot is very far away from us, about 1 billion light-years away, but it is not some kind of celestial body. It is a high-energy burst event - the flash of a gamma ray burst.

This is a deep space image jointly observed by the Gemini Telescope and the Hubble Telescope

In the picture we can see a red dot. This red dot is very far away from us, about 1 billion light years, but it is not some kind of celestial body. It is a high-energy explosion event - the flash of gamma ray burst (GRB211211A).

This gamma ray burst is very special. It is very different from previous bursts.

The discovery of GRB211211A

On December 11, 2021, the Fermi Gamma-ray Telescope captured a very high-energy burst. Its photons carried an energy of up to 1 billion electron volts and lasted for a long time, about more than 50 seconds.

High-energy flash of gamma ray burst

At the same time, Swift Observatory also noticed this burst and determined its location. It came from Boötes , which is more than 1 billion light-years away from us. It is so far away and can have such powerful energy. This is undoubtedly a terrifying burst - gamma ray burst . After

, it was numbered GRB211211A. That is the first gamma ray burst discovered on December 11, 2021.

Gamma ray burst indication

The horror of a gamma ray burst is that it concentrates the energy of the burst into two clusters. If it is strafed by such energy, even thousands or even tens of thousands of light years away, it may bring catastrophe to living things. Fortunately, the gamma ray bursts discovered so far all come from distant galaxies outside the Milky Way . No related event has been found in the Milky Way so far.

But astronomers also mentioned that the explosion of massive stars such as O-type stars and Wolf-Rayet stars in the Milky Way may produce gamma-ray bursts. Among them, the most famous Eta Carinae is a possible source.

The formation mechanism of Eta Carinae about to explode

Gamma ray burst

The burst of gamma ray burst seems to be just a high-energy flash, with no rules to follow. However, after long-term research, we have discovered two categories: long burst and short burst .

Long bursts refer to bursts of more than two seconds, while short bursts refer to bursts of less than two seconds. There are two outbreaks of

, which indicates that there are two different physical mechanisms of and .

Our current general understanding of long bursts is this: it is a supernova explosion that occurs at the end of the life of a massive star. When the supernova explodes, its core collapses into a black hole. The strong gravity of the black hole gathers the debris of the star to form a accretion disk surrounding it. The accretion disk has a strong magnetic field. The magnetic field will eject the falling material from the poles of the black hole to form two jets, thereby forming a gamma ray burst.

Long burst formation demonstration

Short bursts come from the merger of compact binary stars, which are generally considered to come from the merger of neutron stars and neutron stars. This merged burst is called nova .

The formation of short burst indicates

So, the long burst corresponds to the supernova explosion , and the short burst corresponds to the kilonova explosion .

This is the answer we have come from our long-term research on gamma ray bursts.

But the gamma ray burst discovered on December 11, 2021 was not like this. The suspicious point of

GRB211211A is that the duration of

is more than 50 seconds. It is very certain that this is a long storm.

So after the explosion occurred, astronomers quickly thought of observing its afterglow, which is the flash after high-energy electromagnetic waves, such as X-rays , visible light and then infrared band images, to look for signs of supernova .

GRB211106A Short burst afterglow

But after the observation, astronomers were puzzled. They did not find the slow-disappearing and bright afterglow corresponding to a supernova. Its afterglow was very weak, and the infrared image was brighter than the visible light image, and the afterglow disappeared very quickly. This is very similar to the characteristics of nova and .

later searched for its host galaxy and found that it was not within the host galaxy, but on the periphery of the galaxy.

The host galaxy G1 is a certain distance from GRB211211A.

All these signs indicate that is not a supernova, but a kilonova .

Then this becomes very interesting. Our previous understanding of long bursts and short bursts seems to have a new situation.

long bursts do not necessarily come from supernovae, they can also be produced by kilonovae .

But this kind of kilonova does not seem to be an ordinary kilonova.

In December 2022, two papers were published in the magazine "Nature", providing three possible explanations for such a new situation. Among them is the research team led by Zhang Binbin from my country's Nanjing University .

Screenshot of the paper

One explanation is that the merger of two neutron stars did not immediately form a black hole, but first formed a larger neutron star. This neutron star withstood huge pressure for a moment, causing it to collapse into a black hole some time later. This prolongs some time for the energy to be released, creating a long burst.

Another possibility is that this is the merger of a neutron star and a small black hole. When merging with the black hole, the black hole swallowed the neutron star slightly slower.

The third theory is that this kilonova may be the merger of a neutron star and a white dwarf . After their merger, a magnetar was formed. The magnetar has a strong magnetic field, which provides additional energy to the gamma ray burst, thus forming a long burst.

We are still exploring the facts, so we are still not clear about which one it is. However, one thing is certain. Through this research, we know that our previous understanding of gamma ray bursts is only a very small part. Such high-energy flashes seem to only last for tens of seconds, but the physical mechanism of their generation has many unknown mysteries.