Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - imbh (Do intermediate-mass black holes exist?)

Teaser

The consolidator grant focuses on how black holes form and in particular whether intermediate-mass black holes exist (masses intermediate between black holes 10 times more massive than the Sun as typically found in our galaxy, and the super-massive black holes found in the...

Summary

The consolidator grant focuses on how black holes form and in particular whether intermediate-mass black holes exist (masses intermediate between black holes 10 times more massive than the Sun as typically found in our galaxy, and the super-massive black holes found in the nuclei of galaxies of masses more than 1 million times the mass of the Sun). How black holes form is a general problem in astronomy that is not well understood.

This is curiosity driven research. Black holes are objects that capture the mind of many in the public and researchers alike.

The goal is to find intermediate-mass black holes if they exist (not finding those black holes at locations where they are expected is of course also an interesting outcome).

Work performed

\"The work has three aspects (three promising areas in astronomy where we think that we have a good chance of finding intermediate-mass black holes).

1) so called ultra-luminous X-ray sources emit more (X-ray) light than expected for a typical stellar mass black hole of 10 times the mass of the Sun. They do so because they accrete (=\"\"eat\"\") gas from a neighbouring companion star. We are searching for systems where that companion star is a red-supergiant as those are so bright that we can determine their velocities using near-infrared spectroscopy using the largest telescopes on Earth. From those velocities we can deduce the mass of the black hole they circle around. We have finished the survey of nearby ultra-luminous X-ray sources to find those that have a red-supergiant companion star (published Lopez et al. 2017). A second (new) thread of research has opened here after the gravitational wave detectors LIGO/Virgo showed that black holes with masses of 20-40 times the mass of the Sun exist. We have started a project to investigate if such black holes also exist in our galaxy (as so far such black holes were not found in our own galaxy).

2) in the formation of a galaxy like our milky way, many smaller galaxies have merged together. One of the theories on how supermassive black holes form state that those smaller galaxies should have hosted intermediate mass black holes. We are searching for the remnants of those smaller galaxies around our galaxy and around our neighbour galaxy the Andromeda galaxy as those remnants are expected to host the original black hole as well. These systems are called hyper-compact stellar clusters. We have used large ground based surveys for this and we will use Gaia\'s Data Release 2 (that will become public in April 2018). We have also updated and expanded existing simulations on how we expect these hyper-compact stellar clusters to look like in order to have a database of potential images to compare our data with.

3) we use tidal disruption events to assess the mass of the black hole. Tidal disruption events are events where a star wanders too close to a black hole and gets shredded apart by the large difference in gravitational pull between the part close to the black hole and the part facing away from the black hole. Some types of stars namely white dwarfs can only be disrupted by intermediate mass black holes. So we are searching for such events. A fast flare is expected to occur up on disruption of such stars and we have provided the Gaia satellite that happens to gather data that is also suitable to search for such fast flares, with the tools needed to provide the scientific community with information of the occurrence of such flares. In addition, we investigate tidal disruption flares found by other means than by Gaia in order to learn about this new phenomena and to use it as a tool to investigate black holes. We have shown that indeed some of these are caused by intermediate mass black holes (see publication of Wevers et al. 2017).\"

Final results

So far there is only suggestive evidence for the existence of intermediate-mass black holes and through our work we hope that we can provide solid evidence for the existence. Of course as this is research in full swing we have no idea what our results will be at the end of this project.