The First Panchromatic Study of a Tidal Disruption in a Star with a Jet

A female scientist from the Astronomical Institute of the CAS was part of the team that for the first time achieved a long-term observation of an extremely rare event: a stellar tidal rip. Astronomer Christina Thönea was involved through her observing programmes on telescopes located at the Calar Alto Observatory and in the Canary Islands. The Nature journal has now published a paper on the research, called “A very luminous jet from disruption of a star by a massive black hole”.

Tidal Disruption Events (TDEs) occur when an object, often a star, gets too close to a black hole and is torn apart by gravitational forces. This is usually a supermassive black hole, which is found at the centre of almost every galaxy. The tidal forces of the black hole tear the star apart, forming an accretion disk that the black hole gradually consumes. In some, apparently very rare cases (less than 1%), this tidal disruption will even produce a relativistic jet with material ejected from the black hole at very close to the speed of light. The material then glows intensely in the range from radio waves to light to X-rays due to collisions within the jet and collisions with the surrounding environment.

Until now, these so-called "jetted" TDEs have been discovered by high-energy satellites in space. The last time this happened was 10 years ago, in 2012. However, the discovery of AT2022cmc in February this year was different. The paper's first author, Igor Andreoni, developed a method to search for possible events and provide early alert as part of a large-scale ground-based optical survey at the Zwicky Transient Facility (ZTF) located on Mount Palomar in California.

The early alert started a worldwide observing campaign involving X-ray and ultraviolet satellites, ground-based optical and infrared telescopes, and several radio telescopes. Dr Christina Thöne from the Astronomical Institute of the CAS participated in the observations using her observing programmes on the 2.2 m diameter telescope at the Calar Alto Observatory and the giant 10.4 m diameter Gran Telescopio Canarias telescope located in the Canary Islands. The latter telescope was particularly important for obtaining a time series in the infrared, important for determining the evolution of the broadband spectral distribution, i.e. a diagram of what light an object emitted at different frequencies, from radio to X-rays.

Observations showed that the event had two emission components: absolute blackbody radiation from the remnants of the torn star itself, and synchrotron emission from the jet. Broadband observations revealed several changes in these emission components. The spectrum of the event showed that it was located at a cosmological distance of 8.5 billion light-years, or, at a redshift of z = 1.1. The Hubble Space Telescope and radio telescopes have been able to pinpoint the location of the event very accurately, but because the light from the event itself is still shining through its parent galaxy, further observations will be needed to determine where in its parent galaxy the event occurred. Compared to other events that produce jets, such as gamma-ray bursts (GRBs), the gas that absorbs some of the light in specific spectral lines appears to have similar properties, and therefore the galaxies in which the two events happen might not be very different.

The difference in the formation of "normal" and "jetted" TDEs is not yet fully understood. One theory suggests that jetted TDEs require a very rapidly rotating black hole to drive the jet. Future studies will contribute not only to a better understanding of these events, but also to the understanding of the processes in the central black holes of distant galaxies.

The telescopes involved in this work:

- The Palomar 48-inch Samuel Oschin Telescope (Zwicky Transient Facility),

- Liverpool Telescope, Blanco Telescope,

- GROWTH-India Telescope,

- Very Large Telescope,

- Nordic Optical Telescope,

- Very Large Array, Submillimeter Array,

- Northern Extended Millimeter Array,

- James Clerk Maxwell Telescope,

- upgraded Giant Metrewave Radio Telescope,

- Palomar 60-inch Telescope,

- Palomar 200-inch Hale Telescope,

- Asteroid Terrestrial-impact Last Alert System,

- Gran Telescopio Canarias,

- Calar Alto Observatory,

- W. M. Keck Observatory,

- Gemini Observatory,

- Neil Gehrels Swift Observatory,

- Neutron Star Interior Composition Explorer,

- Hubble Space Telescope.

Publication: Igor Andreoni, et al., A very luminous jet from the disruption of a star by a massive black hole, Nature (2023). DOI: 10.1038/s41586-022-05465-8

Original Story Source: Czech Academy of Sciences