Astronomers have observed the central regions of Henize 2-10, a dwarf starburst galaxy previously reported to have a central massive black hole, at optical wavelengths using the Space Telescope Imaging Spectrograph (STIS) on the NASA/ESA Hubble Space Telescope.
Henize 2-10 is located 30 million light-years away in the southern constellation of Pyxis.
Otherwise known as ESO 495-21 and LEDA 24171, this galaxy is just 3,000 light-years across, but it harbors a black hole of about one million solar masses at its core.
“Ten years ago, as a graduate student thinking I would spend my career on star formation, I looked at the data from Henize 2-10 and everything changed,” said Dr. Amy Reines, an astronomer with the eXtreme Gravity Institute at Montana State University.
“From the beginning I knew something unusual and special was happening in Henize 2-10, and now Hubble has provided a very clear picture of the connection between the black hole and a neighboring star forming region located 230 light-years from the black hole.”
That connection is an outflow of gas stretching across space like an umbilical cord to a bright stellar nursery.
The region was already home to a dense cocoon of gas when the low-velocity outflow arrived.
Hubble spectroscopy shows the outflow was moving about 1.6 million kmh (1 million mph), slamming into the dense gas like a garden hose hitting a pile of dirt and spreading out.
Newborn star clusters dot the path of the outflow’s spread, their ages also calculated by Hubble.
This is the opposite effect of what’s seen in larger galaxies, where material falling toward the black hole is whisked away by surrounding magnetic fields, forming blazing jets of plasma moving at close to the speed of light.
Gas clouds caught in the jets’ path would be heated far beyond their ability to cool back down and form stars.
But with the less-massive black hole in Henize 2-10, and its gentler outflow, gas was compressed just enough to precipitate new star formation
“At only 30 million light-years away, Henize 2-10 is close enough that Hubble was able to capture both images and spectroscopic evidence of a black hole outflow very clearly,” said Zachary Schutte, a graduate student in the eXtreme Gravity Institute at Montana State University.
“The additional surprise was that, rather than suppressing star formation, the outflow was triggering the birth of new stars.”
“Hubble’s amazing resolution clearly shows a corkscrew-like pattern in the velocities of the gas, which we can fit to the model of a precessing, or wobbling, outflow from a black hole. A supernova remnant would not have that pattern, and so it is effectively our smoking-gun proof that this is a black hole,” Dr. Reines said.
The new findings were published in the journal Nature.
Z. Schutte & A.E. Reines. 2022. Black-hole-triggered star formation in the dwarf galaxy Henize 2-10. Nature 601, 329-333; doi: 10.1038/s41586-021-04215-6
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