Astronomers detected a burst caused by a black hole swallowing a star

• The cosmic explosion reached its maximum brightness in just 4 days in a small galaxy 500 million light-years away from us
• The team led by Claudia Gutiérrez, IEEC researcher at the Institute of Space Sciences (ICE-CSIC), has used the Gran Telescopio Canarias (GTC) and the Nordic Optical Telescope (NOT), at the Roque de Los Muchachos Observatory, of the Instituto de Astrofísica de Canarias (IAC), in La Palma
• The details of this extraordinary burst have been published in The Astrophysical Journal

An international scientific team has managed to detect an exceptionally fast and bright cosmic burst in a small galaxy located 500 million light years away. This discovery, led by Claudia Gutiérrez, researcher from the Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) at the Institute of Space Sciences (ICE-CSIC), is published today in a study in The Astrophysical Journal.

The burst, identified as CSS161010, reached its maximum brightness in just 4 days and dropped to half in just 2.5 days, which meant that both its discovery and the subsequent observations of its evolution became a scientific milestone and a challenge for the research team.

The CSS161010 event was discovered by the Catalina Real-Time Transient Survey, with a previous detection reported by the All-Sky Automated Survey for SuperNovae. Its subsequent follow-up, which allowed its characterisation, was carried out with the Gran Telescopio Canarias (GTC) and the Nordic Optical Telescope (NOT), both installed at the Roque de Los Muchachos Observatory, of the Instituto de Astrofísica de Canarias (IAC), located in the municipality of Garafía in La Palma.

These types of rapidly evolving cosmic phenomena are very difficult to study due to their nature. However, modern techniques and more advanced instruments make it possible to study them thanks to the improved 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, but their 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 about its physical origin and their analysis suggests that it is actually the image resulting from a small black hole swallowing a star.

This conclusion was reached as the team found broad hydrogen lines showing very high speed—up to 10% of the light speed—and an unprecedented evolution. Two months after the start of the outburst, the object’s brightness had decreased 900 times compared to its maximum. Surprisingly, the spectra captured by the Gran Telescopio Canarias at this time revealed that all the hydrogen line profiles were still blueshifted, which in astrophysics means they are moving towards us at extremely high speeds. This would indicate a strong gas outflow, something completely unforeseen for phenomena such as supernovae.

“We had never found a hydrogen line profile so blueshifted. This feature was both surprising and intriguing, prompting us to investigate possible connections with the galaxy where the event occurred,” says Gutiérrez.

Looking for intermediate mass black holes

The burst occurred in a tiny galaxy containing a mass of stars about 400 times less than our Milky Way’s. Therefore, if the galaxy hosts a massive black hole, its mass must also be small, corresponding to an intermediate-mass black hole.

“So far, this kind of black holes have been extremely hard to identify and astronomers are only aware 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. “Identifying and characterising intermediate-mass black holes is essential for understanding black hole formation pathways and evolution. In fact, they are the fundamental components of supermassive black holes found at the centre of galaxies, and they have been observed to exist even in the early Universe,” adds Professor Mattila.

Professor Peter Lundqvist from Stockholm University, also part of this team, points out: “The disintegration of a star that came too close to the intermediate-mass black hole reveals the black hole, which would be quiescent otherwise. There are likely to be other such black holes in other dwarf galaxies, and we need to track down events similar to CSS161010 in order to determine the properties of these black holes more precisely.”

Press release prepared in collaboration with the Institute of Space Sciences.

More information

This research is presented in a paper entitled “CSS161010: A Luminous, Fast Blue Optical Transient with Broad Blueshifted Hydrogen Lines”, by C. P. Gutiérrez et al., to appear in the journal The Astrophysical Journal on 11 December 2024. DOI:10.3847/1538-4357/ad89a5

Links

• IEEC
• ICE-CSIC
• Gran Telescopio Canarias
• Nordic Optical Telescope

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About the IEEC

The Institute of Space Studies of Catalonia (IEEC — Institut d’Estudis Espacials de Catalunya) promotes and coordinates space research and technology development in Catalonia for the benefit of society. IEEC fosters collaborations both locally and worldwide and is an efficient agent of knowledge, innovation and technology transfer. As a result of more than 25 years of high-quality research, done in collaboration with major international organisations, IEEC ranks among the best international research centres, focusing on areas such as: astrophysics, cosmology, planetary science, and Earth Observation. IEEC’s engineering division develops instrumentation for ground- and space-based projects, and has extensive experience in working with private or public organisations from the aerospace and other innovation sectors.

The IEEC is a non-profit public sector foundation that was established in February 1996. It has a Board of Trustees composed of the Generalitat de Catalunya, Universitat de Barcelona (UB), Universitat Autònoma de Barcelona (UAB), Universitat Politècnica de Catalunya · BarcelonaTech (UPC), and the Spanish Research Council (CSIC). The IEEC is also a CERCA centre.