with files from the National Radio Astronomy Observatory
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Growing up in Wilmington, Delaware, Gregory Sivakoff would try to watch meteor showers, but it hadn?t occurred to him that he might want to be an astronomer until his senior year of high school.
??My father and I were discussing what I liked about science in the car one day when he made a statement that I remember as, ?Have you thought about astrophysics? The universe is really big and that should help you find something to study.??
A little less than two years later, he started research as an undergraduate at Brandeis University. In August 2009, he joined a University of Virginia research team that recently announced very big discovery: a supermassive black hole in a dwarf galaxy.
This April, Sivakoff will continue this work as a newly-appointed assistant professor in the Department of Physics at the University of Alberta. Sivakoff?s research at the U of A will focus on the most extreme objects in the Universe: white drawfs, neutron stars and black holes, such as the one found in the dwarf galaxy.
The galaxy, called Henize 2-10, 30 million light-years from Earth, has been studied for years, and is forming stars very rapidly. Irregularly shaped and about 3,000 light-years across (compared to 100,000 for our own Milky Way), it resembles what scientists think were some of the first galaxies to form in the early Universe.
?Our surprising new discovery of a supermassive black hole in Henize 2-10 hinges strongly on our detection of X-ray emissions thought to be from the accretion disk (the ?ring? of matter that circles the black hole) and radio emission thought to be from a relativistic jet (a jet of plasma thought to be emanating from just outside the black hole at the centre of a galaxy),? says Sivakoff. ?One of the reasons why studying the connection between accretion discs and relativistic jets is important is that astronomers currently believe that the relativistic jets from supermassive black holes may play an important role in how galaxies form.?
Sivakoff led the analysis and interpretation of X-ray data for the Henize 2-10 observation team. The group was led by University of Virginia graduate student Amy Reines, under the supervision of her thesis advisor, Kelsey Johnson of the University of Virginia and the National Radio Astronomy Observatory (NRAO), and Crystal Brogan of the NRAO.
?As part of her thesis, Amy was originally looking at this galaxy with optical/near-infrared and radio data to study the young clusters of stars created in this dwarf galaxy with intense star formation,? says Sivakoff. ?To her surprise, she began to suspect something even more interesting was going on in Henize 2-10; she began to think that the central radio source might actually be a supermassive black hole, a black hole with much more mass than the Sun (typically millions to billions times that of the Sun).?
?My first thoughts were that of a healthy skeptic,? Sivakoff recalls. ?I thought the X-ray emission was probably coming from a stellar mass black hole, a black hole approximately the mass of the Sun, that was accreting the outer atmosphere or wind of a companion star. But this hypothesis just did not fit the radio data; no X-ray binary is as radio bright as the source in Henize 2-10.?
Supermassive black holes lie at the cores of all "full-sized" galaxies. In the nearby Universe, there is a direct relationship -- a constant ratio -- between the masses of the black holes and that of the central "bulges" of the galaxies, leading them to conclude that the black holes and bulges affected each others' growth. However, it is difficult to speculate on the mature size of a developing galaxy.
?It's actually very hard to predict the growth of Henize 2-10,? says Sivakoff. ?There are too large a number of variables that I would feel comfortable making a secure prediction.?
Sivakoff will continue to monitor the dwarf galaxy as a member of the Reines team.
?We are taking new data to better test how the X-ray properties of the black hole in Henize 2-10 compare to actively accreting supermassive black holes,? he says.
?There are also ongoing efforts to search whether a more accurate mass measurement for the black hole is possible at radio wavelengths. An additional unanswered, but important, question that we plan to answer in the near future is whether the star formation activity in Henize 2-10 is related in any way to the supermassive black hole. ?
Sivakoff says the research will point to even bigger things.
?It's not just this monitoring galaxy that is important; it's the new window in galaxy evolution this is opening up. We plan to search for supermassive black holes in other galaxies like Henize 2-10 to determine whether supermassive black holes in these galaxies are rare or common. On the theoretical side, astronomers will now need to ensure that models of black hole growth and galaxy growth can make galaxies like Henize 2-10 with supermassive black holes.?
And that should give Sivakoff plenty to study.
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