By IVÁN JIMÉNEZ
Michela Mapelli, a researcher at the Padua astronomical observatory, belonging to the INAF, is interested in the forces at work in galaxies, and especially in the dark side of our Galaxy, the Milky Way. The problem of our Galaxy is that when you try to get to the heart of it you end up rather frustrated. As well as being in a difficult position to study it,- right in the plane, and about half way from the centre to the edge, the main obstacle is interstellar dust which blocks our line of sight to the Galactic nucleus, where there is a very strong indication that a supermassive black hole is present. Because of this the Galactic centre is one of the most mysterious places for an astrophysicist.
However studying it is basic if we want to get to the bottom of how the galaxy works. Luckily in astronomy when you can´t see something you can often find another approach. For Michaela the best way to get to understand the galactic centre is to use numerical simulations, that is by making models on the computer. Only this way can anyone try to run backwards in a few seconds the whole of the lengthy history of our galaxy. Recently Michaela has been awarded the prestigious MERAC award wih the European Astronomical Society gives to the best research career of a young astronomer. This is undoubtedly a deserved recognition for the scientific achievements achieved at such an early stage but, as she herself says, it is also a spur to keep on working during a moment when another black hole, the economic crisis, is undermining the hopes of many scientists.
What do we currently know about the galactic center of the Milky Way than a few years ago we could not imagine? Is our galaxy more active than we thought?
Our knowledge about the galactic centre is in continuous expansion. I will mention just one example, which is very important for my work. A few years ago, most astronomers believed that the young stars we observe in the central parsec did not form 'in situ'. Currently, not only we are reasonably convinced that they formed in situ, but there are several hints that star formation is still ongoing and that even protoplanetary discs exist in the central parsec of our galaxy!
What role does the black hole in the galactic center play? How does it affect the structure of our galaxy and star formation?
The black hole at the centre of our galaxy seems to be a very quiet and nice guy: no large-scale jets, no strong outflows, it radiates at very low level. Of course, we do not know whether, sometime in the past, the black hole was 'active', i.e. it radiated energy at higher level. On the other hand, even if it is now quiescent, our black hole has a mass of several million solar masses, confined in a very small region. This means that it exerts a strong tidal field on whatever approaches the centre of our galaxy. In particular, molecular clouds are expected to be disrupted in the innermost parsec. Since stars are thought to form from the collapse of dense clumps in molecular clouds, this implies that stars cannot form 'in normal conditions' too close to the black hole. However, it seems that there are some peculiar pathways, able to form stars even in extreme conditions. This is the main topic of my study.
Is it possible that stars in the galactic centre harbour planets?
Understanding whether planets can form and manage to survive in the galactic centre is the main topic of one of my ongoing projects... Observational signatures of photoevaporative protoplanetary discs have recently been published, but we do not know whether such protoplanetary discs can survive and form planets.
In my recent paper, we do not address the difficult question whether planets can form in the galactic centre, but we assume that they do, and we study the possibility of observing them. Our main conclusion is that, if planets exist in the galactic centre, they might have properties similar to the G2 cloud, and they might be observed with current facilities (8m class telescopes) under some conditions.
Astronomy is commonly associated with observing the sky. However, is not widely know the importance of the use of simulations. To what extent are simulations a useful tool in astronomy?
Simulations are a must in astrophysics, for many reasons. First, most astrophysical processes occur on a timescale that is much longer than human life: we cannot observe the live evolution of a galaxy, but we can simulate it in a few days. Simulations are essential to reconstruct the 'timeline' of what we observe. We could say that observations alone give us the tip of a iceberg, while the combination of observations and simulations can reveal the entire thing.
Furthermore, many astrophysics processes are too complex to be investigated analytically. In many cases, simulations enable us to reach a level of complexity that cannot be achieved otherwise.
How numerical simulations can help us study the center of our galaxy? Do current simulations complement well with recent observations of the galactic center?
The galactic centre is a perfect example for both my considerations. Today, we observe several hundred young stars in the galactic centre, but young means 3 Myr old, i.e. they formed much earlier than the first appearance of men on earth!
We do not know which were the conditions of our galactic centre 3 Myr ago. For example, we do not know whether molecular gas lied in the central parsec, but we can simulate different molecular clouds in the galactic centre (with different masses, orbits, etc) and see which of them produce 'stars' with properties similar to the ones that we observe now in the galactic centre.
Before we were able to run such simulations, analytic models already predicted the possibility of forming stars during the disruption of molecular clouds, but it is only thanks to simulations that we can include several processes (such as gas cooling and heating, shocks, radiative transfer, etc.) in the overall picture, and obtain important constraints.
What remains to be done? Do we know well the structure and evolution of our galaxy?
This question is short but the answer might be very long..and I am not the best person to answer. I will try to answer a slightly different question, on a more limited topic, that is 'do we know well the structure and evolution of our galactic centre'?
The galactic centre is one of the most studied -and yet one of the most enigmatic- places in the Universe. One of the main unanswered questions is: 'Why is our supermassive black hole so quiescent with respect to the supermassive black hole candidates hosted in nearby galaxies? Has it always been like this?'
I am sure that understanding the physics of gas and the process of star formation in the innermost parsecs can give us the clue to answer this question. The previous activity of the black hole might be 'written' on the history of star formation of our galaxy, but theorists and observers have a lot of things to do before finding this clue..
Despite your youth, you have an excellent CV. What has it been the most satisfactory experience as a researcher for now?
I never thought about this… There are several good candidates. Having been awarded the MERAC prize is the most recent one. The day I started creating my own research group is another one. The day I published my first paper as first author (back in 2004, during my first year of PhD) is probably the first satisfactory experience of my career.
Recently you have been awarded by the European Astronomical Society with the MERAC Prizes for the Best Early Career Researcher. What does this recognition mean to you?
This recognition has an extraordinary value for me. It is the best possible recognition of my research achievements, so far!
Being researcher in Italy, during the economic crisis, is not an easy task: I have to struggle with the contraction of funding for research, I see my colleagues (even the best ones) quitting the academic career because there are no jobs. Sometimes, I feel quite discouraged. The MERAC prize gives me motivation to continue my research, with new impulse and enthusiasm. I am more optimistic about my future chances and opportunities. This prestigious award is the best possible way to start a second, more mature, phase of my career. I could not have dreamed of a better start.
Video interview here.
