The Death Of Massive Stars Creates Black Holes And Neutron Stars

The supernova explosion of a massive star can create the most compact and mysterious objects in the universe: very dense neutron stars and black holes. For the first time, astronomers were able to observe it directly in a neighboring galaxy.

There is therefore a direct connection between the explosive death of massive stars and the formation of the most compact objects in the universe, namely black holes and neutron stars. This was demonstrated for the first time through direct observation: two teams studied the aftermath of a supernova explosion in a neighboring galaxy and were able to find important information about the mysterious compact object it left behind. Her work has been published in Nature and The Astrophysical Journal Letters.

At the end of their lives, when they have burned all their fuel, massive stars collapse in on themselves under the action of their own gravity, creating a gravitational singularity; Then an extremely violent explosion occurs, a so-called supernova (see box). A very rare catastrophic phenomenon: the last one in our galaxy, the Milky Way, dates back four centuries ago.

And what remains after such an explosion? Astronomers believe that the star leaves behind only a compact remnant, its ultra-dense core: depending on the star's mass, it is a neutron star or a black hole. A neutron star is so dense that a teaspoon of its material would weigh about a trillion kilograms on our Earth! As for the black hole, with its infinite density, not even light can escape.

>> Also read: Humanity sees a black hole with its own eyes for the first time in history

>> The supernova SN 2022jli, discovered in May 2022, before and after its explosion:

The supernova SN 2022jli in the spiral arm of the neighboring galaxy NGC 157, 75 million light-years away, before (a) and after (b) its explosion. [Ping Chen & al. – Nature]

A two star system

It is not uncommon for massive stars to orbit a companion star in a so-called binary star system; The star behind the supernova SN 2022jli is no exception to the rule. What is notable here is that the companion star apparently survived the violent death of its partner and that the two objects, the compact remnant and the companion star, probably continued to orbit each other.

>> The ballet of a companion star and the dense object resulting from the supernova:

This artist's impression shows the process by which a massive star within a binary star system goes supernova. After the catastrophic explosion, the original star leaves behind a compact object: a neutron star or a black hole. The companion star survived the explosion, but its atmosphere expanded. The compact object and its companion star continue to orbit each other; The compact object regularly steals matter in the star's inflated atmosphere. This accumulation of matter was observed in the research teams' data in the form of regular fluctuations in brightness as well as periodic fluctuations in hydrogen. [L. Calçada – ESO]

Astronomers observed that after this supernova exploded, the companion star's atmosphere swelled and became enriched with the hydrogen gas left behind from the explosion. As the cosmic ballet between the two entities continued, scientists found that the compact object was continually extracting material from the supernova's atmosphere and forming a hot disk with that material around itself. This enrichment generates a lot of energy.

This causes periodic fluctuations in hydrogen as well as variation in luminosity: “This is the first time that repeated periodic oscillations over many cycles have been detected in the light curve of a supernova,” notes Thomas Moore, a doctoral student at Queen's University in Belfast, Northern Ireland, in the study he led, quoted in a press release from the European Southern Observatory (ESO). Gamma ray bursts from the binary star system have also been observed.

This real-time observation of the phenomenon provides “a direct link” to this compact remnant, as Ping Chen, a researcher at the Weizmann Institute of Science in Israel and lead author of one of the studies, emphasizes.

Now that the presence of a black hole or neutron star has been confirmed, scientists still have much to discover about this enigmatic system, including the exact nature of the compact object or the end that might await this binary system. According to ESO, next-generation telescopes such as the Extremely Large Telescope, due to enter service by the end of the decade, will help enable astronomers to reveal unprecedented details about this unique telescope and many others.

>> A video and an English summary of the discovery:

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Stephanie Jaquet