They detect a rare explosion when a black hole devours a star

Dec. 12 () –

An international team of astronomers has managed to detect an exceptionally fast and bright cosmic burst of unknown origin in a small galaxy 500 million light years away.

The burst, identified as CSS161010, reached its maximum brightness in just four days and halved in just 2.5 days, making both its discovery and subsequent observations of its evolution a scientific milestone. and a challenge for the research team. The discovery is reported in the magazine The Astrophysical Journal.

Event CSS161010 was discovered by the Catalina Real-Time Transient Survey, with a previous detection reported by the All-Sky Automated Survey for SuperNovae. Its subsequent monitoring, which has allowed its characterization, has been carried out with telescopes such as the Gran Telescopio Canarias (GTC) and the Nordic Optical Telescope (NOT), both installed at the Roque de Los Muchachos Observatory, of the Institute of Astrophysics of Canary Islands (IAC).

These types of rapidly evolving cosmic phenomena have been very difficult to study due to their nature. However, modern techniques and more advanced instruments allow them to be studied thanks to the improved field of view and the ability to capture high-resolution images from the telescopes used.

To date, only a dozen cosmic explosions with these characteristics in terms of brightness and evolution have been detected, but its origin remains a complete mystery. However, the team of researchers led by Claudia Gutiérrez believes that, for the first time, the unique spectral properties of CSS161010 provide important clues to its physical origin and their analysis suggests that it is actually the result of a small black hole swallowing a star.

The team reached this conclusion by finding broad lines of hydrogen that showed very high speeds, up to 10% of the speed of light, and an unprecedented evolution. Two months after the start of the explosion, the object’s brightness had decreased 900 times from its maximum.

Surprisingly, the spectra captured by the Gran Telescopio Canarias at that time revealed that all the profiles of the hydrogen lines were still blue-shifted, which in astrophysics means that they are moving towards us at extremely high speeds. This would indicate a strong outflow of gas, something completely unexpected for a supernova.

“Discovering and analyzing these cosmic explosions is particularly challenging due to their rapid evolution. However, the agile response of our scientific collaboration allowed us to obtain high-quality spectra. These data revealed unique properties never observed in any other object, allowing us define the nature of this extraordinary event,” explains in a statement Claudia Gutiérrez, lead author of the study and postdoctoral researcher at the Institute of Space Studies of Catalonia (IEEC) and the Institute of Space Sciences (ICE-CSIC).

“When we saw the specters, we didn’t know what to say,” says Gutierrez. “We have never found such a blue-shifted line profile of hydrogen; this shift would mean that the gas is moving towards us at extremely high speeds. This feature was both surprising and intriguing, and prompted us to investigate possible connections with the galaxy where the event occurred,” he adds.

The burst occurred in a tiny galaxy that contains a mass of stars about 400 times less than that of our Milky Way. Therefore, if the galaxy hosts a massive black hole, its mass must also be small, corresponding to a black hole of intermediate mass (100-100,000 solar masses).

“Until now, these types of black holes have been extremely difficult to identify, and astronomers only know of a very small number of confirmed cases,” explains Professor Seppo Mattila, from the University of Turku in Finland, one of the lead authors of the paper.