Search for the all-consuming emptiness...

As early as the 18^th century, the English natural philosopher John Michell suggested that ‘there might exist stars much larger than the sun, for which the escape velocity well exceeds the speed of light.’ Two centuries later, towards the end of the 1960s, one John Archibald Wheeler coined the term ‘black hole’ for an imploded star with an irresistibly strong gravitational pull. Not long after one was found: Cygnus X-1.

One heavy trip

Cygnus X-1 is a so-called ‘binary system’: a blue star coexisting with a compact object. The compact object has a mass of about 8.5 times that of the sun (the mass of the sun is approximately 2 x 10³⁰ kg), but a volume of only 0 m³! If you were to wander within range of the so-called ‘event horizon’ of this gaping hole, your (final) destination would be certain. ‘One way ticket to the core, please.’ This core is a point of infinitely high density and infinitely low volume and the journey to it would not be very comfortable at all...

Large and small black holes

There are various kinds of black holes, each with a different mass. Sagittarius A*, the black hole in the middle of the Milky Way, has an estimated mass of 3.3 million times that of the sun. But there are also hypothetically miniature black holes with masses approaching the Planck mass (approximately 2 x 10^-8 kg). The black hole of Cygnus X-1 is fairly run-of-the-mill: not too big, not too small and very common. It’s one of the stellar black holes, which occur when a star collapses. The origins of supermassive black holes like Sagittarius A* are completely unknown. It is possible that they might have been created during the very beginnings of the star system itself, but it is also plausible that the black hole evolves alongside the star system.

Research in Groningen

Understandably, the origins of these supermassive holes are one of the hot research topics here in Groningen. In fact, astronomers at the Groningen Kapteyn Institute have been studying the origins and structures of star systems for more than a century. The Milky Way was originally one of the favourite subjects, but today our researchers study all manner of star systems to discover more about their evolution. They are carrying out extensive research on black holes and their role in the evolution of star systems. For example, they want to know what influence black holes have on the star systems they inhabit. There are indications that the energy produced by black holes in their active phase can inhibit the formation of stars in the system. And why are some black holes so active, emitting huge amounts of energy, while others appear to be ‘quiet’? In other words: what turns a black hole on and off?

Space quest for black holes

So there are plenty of questions, but how do you go about studying phenomena such as these? Black holes are light years away from us, often hidden behind interstellar dust clouds and, even worse, they are invisible! These gaping chasms emit absolutely no radiation, because not even light can escape from a black hole. So you can’t see them. Of course, we have found solutions to get around this. In the first place, those clouds of dust are easily penetrated with high-tech equipment. After that you need only study the surrounding stars. A star circling a huge blank space at an unusually high speed could indicate the presence of a black hole. Or better yet, you could witness an actual ‘engulfment’, as a star falling into a black hole emits a bright light before being extinguished.

Your own virtual quest

Do you want to search for black holes? You can at Science LinX! We have installed an observation dome on top of the building especially for our visitors. In this observatory our staff will help you to scan the heavens for black holes and other obscure objects. Would you rather not leave your comfy chair at home, or do you want to practise before your visit to Science LinX? Then our special black hole website is a must-see. You can use this site to comb through a virtual universe and read all about the different black holes you discover. You can also take a virtual trip to a black hole and find out what would happen if you fell in... Our researchers have painstakingly calculated how you will be stretched like a strand of spaghetti because the pull on your feet will be stronger than the pull on your head.

Hole filled with questions

Thanks to all our observations, measurements, calculations and virtual journeys, our search for black holes has produced a great deal of information. We know that they exist, that there are several kinds and that they exert a strong influence on the surrounding environments. However, there is still much to be learned. The most intriguing question is what exactly happens in the core of a black hole and what happens to all the objects it engulfs... Any volunteers?

Links

Acknowledgements

Special thanks to: Gijs Verdoes Kleijn, Gergö Popping (Kapteyn Institute), Roeland van der Marel (Space Telescope Science Institute) and Robert Wielinga (Sonnenborgh). Please contact Science LinX if you should have been included in the acknowledgements.

Author

Siëlle Gramser