Astronomers of KFU will take part in the huge Spektr-RG project in 2 years.
What this project really is – this is what we wanted to find out (among other things) during our interview with Ilfan Bikmaev, Professor at the Department of Astronomy and Cosmic Geodesy.
- Dr. Bikmaev, why does Kazan University plan to partake in Spektr-RG?
- First of all I want to remind all of our readers that in order to fully study X-ray emitting space objects we have to observe them in the visible spectrum. X-ray telescopes don’t have sufficient angular resolution to pinpoint the exact objects.
We have the RTT-150 telescope stationed in Turkey. Knowing about that, our colleagues from the Space Research Institute of the Russian Academy of Sciences suggested that we take part in the new project. We have been using RTT-150 to monitor X-ray emissions for 10 years now.
This research resulted in a publication in Astronomy and Astrophysics. The publication stated that SS 433’s mass is thrice that of the Sun’s and thus SS 433 must be a black hole and not a neutron star.
- How do the University’s astronomers prepare for the upcoming work?
- We will need experts in the field. We don’t have them yet, so this past year we opened the X-Ray Astronomy Lab to start teaching them. Leading Russian and foreign researchers will take part in the process, among them Sergei Fabrika.
These days we plan to send our students and employees to intern at the Max Planck Institute which is known for its work in X-ray astronomy. They have amassed a sizable chunk of data during their work. We, on our side, can share the data obtained with RTT-150.
The objects researched by Dr. Fabrika’s group were found by X-ray telescopes. Optical telescopes would have mistaken them for regular stars. But X-ray telescopes, in turn, cannot determine exactly what type of objects they see. So powerful optical telescopes are needed in the end.
- Why is studying cosmic X-ray emissions important?
- X-ray emitting objects have unusual properties, such as very high density and high temperatures. So they are either a new class of objects or known objects in an active phase of some process that makes them heat up to millions of degrees.
- Black holes come to mind…
- Correct, they are included here. We still don’t know the structure of black holes and what happens beyond the event horizon but we know that their gravity is so high that even photons cannot escape them. That’s why finding single black holes is so difficult – they don’t emit any information.
Nevertheless, there is something we know about these mysterious objects. For example, they have axial rotation and therefore – poles and an equator.
- How was this discovered?
- First of all astronomers found binary star systems. Heavier stars evolve faster. In binary systems one of the stars evolves fasters, turns into a supernova and then a black hole.
We are able to find them thanks to their neighbors – less massive stars. A black hole starts consuming matter from its neighbor. This process is gradual. The matter forms an accretion disk around the hole. This is a third object in the system that is studied by scientists.
- What happens inside such a disk?
- Many interesting things. Accretion leads to huge energy outbursts – in the form of optical, ultraviolet and X-ray radiation, radio waves.
- Evidently, this is a consequence of nuclear reactions?
- Probably, but nuclear reactions also require some other conditions, such as very high density.
- Black holes are very dense…
- Yes, but we still don't know what happens on it, so the question of if there are any nuclear reactions inside accretion disks is still out there. We still study what’s outside of a black hole, because holes themselves are still beyond our reach. But we already know what happens between a hole and its disk.
- Probably something very interesting…
- Definitely – holes throw the accretion disks’ matter back into space. Not only as radiation but also as 2 narrow jets emitted from the poles. By the way, accretion disks are positioned along their holes’ equator – just like the rings of Saturn. The jets contain metal nuclei, protons and electrons. They are emitted at near-light speeds and can travel as far as 100 light years.
What is also interesting – all accretion disks are incredibly luminous, emitting millions of times more energy than stars, especially X-ray radiation. This was proven by Soviet researchers Rashid Sunyaev and Nikolai Shakura. Their famous article in Astronomy Letters has been cited tens of thousands of times and is the most cited paper in the history of astronomy by now.
- You mentioned that neutron stars have up to 2 solar masses, and black holes – more than 3. Are there any objects positioned between them in this regard?
- Unfortunately, nothing has been found so far. But if they are found, that will be a huge sensation. This pertains to hypothetical quark stars, for example. But there can be neutron stars with such masses as well. Astrophysicists think that those can be as small as 15 km in radius, but their density equals that of an atomic nucleus.
- So we can say that a neutron star is an “embryo” of a black hole?
- You can say that. If a neutron star is more than 1.5 times heavier that the Sun, sometimes there is an as of yet unknown process leading to its collapse, and the any information from the objects just ceases to be produced because its gravity doesn’t let anything out – photons and even stars as well.
- So those are super-dense black holes?
- No, they are supermassive. We divide them into galaxy mass and stellar mass black holes. The latter ones evolve from stars of 3 to 40 solar masses. They ended their life cycles by turning into supernovas. Most of the star matter was thrown out into space, and the remainder collapsed.
The former ones can weigh up to billions times more than the Sun. It’s still unclear how they come to be, how does such an immense mass gather in a relatively small volume (their size is approximately that of the Solar system). Otherwise they are just usual black holes. They also can have accretion disks – only they are composed of galaxy gas and not of star matter.
Here we have a paradox: according to known laws galaxy gas must be emitted into intergalactic space. But it remains still, and we don’t know why.
In the second part of this interview Dr. Bikmaev will take us further into the secrets of “space cuisine”, especially dark matter.