Joey Neilsen

MIT Kavli Institute for Astrophysics and Space Research


You’ll find on this page some detailed information about my press releases. Don’t forget to check out the links to the real press releases!

Erratic Black Hole Regulates Itself

GRS 1915+105 is an extraordinary 14 solar-mass black hole in our Galaxy. Its relativistic jets and other similarities to actively feeding supermassive black holes (quasars) has earned it the title “microquasar.” Its bizarre brightness variability (below) has earned it the description “pathological.”

The relativistic jet in GRS 1915+105 is choked off as a highly-ionized wind drains its matter supply! (Credit: NASA/CXC/A. Hobart)

In order to understand the physics and plasma processes driving this extreme variability, I analyzed ~10 years of high-resolution spectra from Chandra. By comparing signatures of relativistic jets (broad iron emission lines) and highly-ionized winds (narrow, blueshifted absorption lines) I showed that the wind carries enough mass away from the black hole to halt the flow of matter into the jet! This is illustrated in the movie above.

The result demonstrates that (1) ionized winds may be a very important part of the accretion flow, and (2) stellar-mass black holes like GRS 1915+105 may regulate their accretion rate like supermassive black holes. See Neilsen & Lee, 2009, Nature, 458, 481 for details!

Taking the Pulse of a Black Hole System

But GRS 1915+105 is known for more than its jets and its winds: it is one of the most variable X-ray sources that we know of! Check out this beautiful representation of the ‘Heartbeat State,’ which is one of fourteen such types of variability seen in GRS 1915+105! Looks kind of like an EKG, huh?

The X-ray lightcurve of GRS 1915+105 in its ‘heartbeat’ state.  (Credit: NASA/CXC/J. Neilsen & A. Hobart)

Where does this variability come from and what does it mean? To answer these questions, we figured out a way to study the physical processes at each part of the heartbeat. We found that the wind may carry 95% of the infalling mass away from the black hole... that’s equivalent to 1/3 of the mass of the moon per day!!!

We also realized that the heartbeat can be understood as a battle between radiation and gravity, where radiation tries to push gas away from the black hole and gravity acts to pull it in. This is illustrated in the zoom-in on the inner accretion disk below. As more gas falls in, the inner disk gets brighter and radiation pushes it away from the black hole (panels 1-3). But finally gravity wins, and the gas plunges inwards, leading to a bright flash of X-rays!

This sequence of four illustrations shows the black hole in GRS 1915 and the inner part of the disk surrounding it. (Credit: NASA/CXC/M. Weiss)