They capture the explosion caused by a black hole swallowing a star

Scientists have managed to capture a peculiar explosion in a small galaxy located 500 million light-years away.

The work has been carried out by an international team led by the Institute of Space Sciences (ICE, dependent on the Higher Council for Scientific Research (CSIC) in Spain) and the Institute of Space Studies of Catalonia (IEEC).

The burst, identified as CSS 161010, reached its maximum brightness in just 4 days and decreased by half in just 2.5 days, something completely unusual and which led to both its discovery and the observations following its evolution becoming a scientific milestone and a challenge for the research team. The main author of this work is Claudia Gutiérrez, researcher at ICE and IEEC.

The CSS 161010 event was discovered by the CRTTS (Catalina Real-Time Transient Survey), with a previous detection reported by the ASAS-SN (All-Sky Automated Survey for SuperNovae). Its subsequent monitoring, which allowed its characterization, was carried out with different telescopes, including 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 the Canary Islands ( IAC), located in the municipality of Garafía, in La Palma, Spain.

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

To date, only a dozen cosmic explosions with these characteristics in terms of brightness and evolution have been detected, and their origin remains a complete mystery. However, the team led by Claudia Gutiérrez considers that, for the first time, the unique spectral properties of CSS 161010 give important clues about its physical origin. The analysis carried out based on these clues and other data suggests that it is a small black hole swallowing a star.

This conclusion was reached because the analysis found 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 burst, the object’s brightness had decreased 900 times from its maximum. Surprisingly, the spectra captured by the Gran Telescopio Canarias at this time revealed that all the hydrogen line profiles were still blue-shifted, which in astrophysics means that they are approaching 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 especially difficult 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, which allowed us to constrain the nature of this extraordinary event,” explains postdoctoral researcher Claudia Gutiérrez.

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

In search of intermediate mass black holes

The explosion 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, which corresponds to a black hole of intermediate mass (between 100 and 100,000 times the mass of the Sun).

“Until now, black holes of this type have been extremely difficult to identify and astronomers are only aware of a very small number of confirmed cases,” explains Professor Seppo Mattila, from the University of Turku (Finland), one of the lead authors. of work.

“Identifying and characterizing intermediate-mass black holes is essential to understanding the formation pathways and evolution of black holes. In fact, they are the fundamental components of the supermassive black holes found in the center of galaxies, such as our Milky Way, and whose existence has been observed even in the early universe,” adds Professor Mattila.

Recreation of the explosive phenomenon, identified as CSS 161010, in which a black hole engulfs a star. (Image: Gabriel Pérez / IAC)

For his part, Professor Peter Lundqvist, from Stockholm University, also a member of this team, adds: “The way in which the linear emission evolves in this object resembles that observed in active galactic nuclei, where it is known that supermassive black holes exist. “This similarity provides strong evidence that CSS 161010 also hosts a black hole, albeit not a very massive one.”

Lundqvist notes: “The disintegration of a star that came too close to the intermediate-mass black hole reveals the otherwise quiescent black hole. “There are likely other black holes of this type in other dwarf galaxies, and we need to track events similar to CSS 161010 to be able to more precisely determine the properties of these black holes.”

“Telescopes that scan the sky at high cadence will be crucial to discovering more of these rare and rapidly evolving phenomena,” says Gutiérrez, adding: “Meanwhile, state-of-the-art spectrographs installed on ground-based telescopes like the ones we have used in the Roque de los Muchachos Observatory, in La Palma, will play a crucial role in its characterization. “We are on the cusp of an era full of revolutionary discoveries.”

The study is titled “CSS 161010: A Luminous Fast Blue Optical Transient with Broad Blueshifted Hydrogen Lines.” And it has been published in the academic journal The Astrophysical Journal. (Source: ICE/CSIC)