Generous Stars, Greedy Compact Objects


This week I interviewed Francesca Valsecchi, a graduate student at Northwestern in physics and astronomy, to preview her upcoming Junior Science Cafe event on February 18.

She studies the evolution of stars and their eventual endpoint - compact objects. Once a star runs out of nuclear fuel, which it burns throughout its lifetime, the star collapses on itself. Depending on the star's size, it can become a white dwarf (the smallest compact object), a neutron star, or a black hole (the largest, and my personal favorite). Compact objects are very, very dense, but since they are no longer burning any fuel, they're difficult to observe.

So, Francesca and other researchers learn about stars and compact objects by observing X-ray binary systems - in this case, a compact object coupled with a star. The star feeds, or transfers, mass to the compact object, making the compact object "X-ray bright" - a source of radiation that researchers can "see." Mass transfer can also occur between two stars in a system as they're evolving.

During our interview, she showed me a really cool animation that depicts this mass transfer phase. It shows a star comparable to the size of our Sun evolving in a binary system with a neutron star (the middleweight of compact objects). As it evolves, the star expands, and eventually begins transferring mass to the neutron star. Finally, the star expends all of its energy, collapses on itself, and becomes a white dwarf (the lightweight).

If you want to learn more about black holes, there's a number of articles on SiS that you can check out - my interview with Francesca, an interview with her advisor, Vicky Kalogera, on gravitational waves generated by black holes, and finally a piece about the Large Hadron Collider that includes a bunch of valuable information, including why the LHC is not going to create a black hole that will eat up the Earth. (I promise.) Or, just head to Francesca's Junior Science Cafe event on February 18.

(Animation credits -Stellar simulation: Vicky Kalogera, Bart Willems, Francesca Valsecchi, Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), and Northwestern University, Department of Physics and Astronomy; Visualization: Matthew McCrory, Northwestern University Academic & Research Technologies)




So cool, now if we could just find some way to transfer our own mass to some compact object, we could eat whatever we wanted!

Great blog, Beth!

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