Flares from the Milky Way’s Supermassive Black Hole

An artist's impression of a gas cloud as it passes the black hole at the center of the Milky Way.
Artist’s impression of the disruption of a gas cloud because it passes near Sgr A*, the supermassive black hole at the middle of our galaxy.
ESO / MPE / Marc Schartmann

In 2019, the supermassive black hole at the middle of our galaxy wakened and emitted a sequence of burps. A brand new examine now examines what meal could have led to this indigestion.

Waking Up for a Snack

An artist's impression of the dramatic outflows from an active galaxy’s nucleus.
Artist’s impression of the dramatic outflows from an lively galaxy’s nucleus. The Milky Way’s supermassive black hole, in distinction, could be very quiet.
NASA / SOFIA / Lynette Cook

Sgr A*, the 4.6-million-solar-mass black hole that lies at the middle of the Milky Way, is often a reasonably quiet beast. The black hole slowly feeds on accreting materials in the galactic middle — however this meals supply is sparse, and Sgr A*’s accretion doesn’t produce something like the fireworks we affiliate with supermassive black holes in lively galaxies.

In May 2019, nonetheless, Sgr A* all of a sudden grew to become considerably extra lively than standard, producing an unprecedented brilliant, near-infrared flare that lasted roughly 2.5 hours. This flare was greater than 100 occasions brighter than the typical emission from Sgr A*’s informal accretion, and greater than twice as brilliant as the brightest flare we’ve ever measured from our neighborhood monster.

The May 2019 flare marked the begin of extended elevated exercise — an uncommon variety of sturdy flares that continued at the least all through 2019 (presently analyzed knowledge extends solely to the finish of that year). What brought on Sgr A* to get up? And can we anticipate extra flaring forward? A brand new examine by Lena Murchikova (Institute for Advanced Study) explores the choices.

Shedding Sources

The orbits of several S stars at the center of the Milky Way
Reconstruction of the orbits of a number of S stars at the middle of the galaxy. The two coloured orbits mark two stars with the closest identified approaches to Sgr A*.
Keck / UCLA Galactic Center Group

Sgr A*’s flares doubtless got here from an abrupt improve in the quantity of fabric accessible to accrete onto this black hole. Murchikova identifies two doubtless sources of this extra materials.

  1. Shedding S stars
    The dense nucleus of our galaxy hosts a inhabitants of stars on tight orbits round Sgr A*. These stars shed mass through stellar winds, and when the stars swing shut round Sgr A* at the pericenter of their orbit, this shed mass may accrete onto Sgr A*.
  2. Disintegrating G objects
    Also identified to orbit near Sgr A* are so-called G objects. These prolonged sources could also be gas clouds, stars, or a mix of the two — we’re undecided but! Tenuous G objects lose mass on account of friction as they orbit, exhibiting larger charges of mass loss as they get nearer to Sgr A* and are stretched out into shapes with massive surfaces areas passing by dense background materials. The mass they lose by this disintegration at pericenter may then accrete onto Sgr A*.

Short-Lived or Long-Term?

This image shows the position of objects G2 and G1 and the S2 star relative to Sgr A*.
The objects G2 (coloured red) and G1 (coloured blue) and the star S2 are seen in these high-resolution pictures of the galactic middle, taken in 2006 (left) and in 2008 (proper). The place of Sgr A* is marked with an X.
NASA / SOFIA / Lynette Cook

Through a sequence of calculations, Murchikova estimates how a lot materials is shed by these two forms of objects and the way lengthy it could take that materials to accrete onto Sgr A*. Based on the accessible observations, the creator finds that the more than likely clarification for our black hole’s sudden rumblings in 2019 is presently accreting materials from the mixed previous pericenter passages of the objects G1 and G2.

If this interpretation is appropriate, we might anticipate to see flaring proceed for a restricted time, however Sgr A* ought to then return to its quiescent state. If the flaring was as a substitute part of regular variability in the circulation of accreting materials onto Sgr A*, we might anticipate the exercise to proceed for years to return. Continued observations of this rumbling big will inform!


“S0-2 Star, G1- and G2-objects, and Flaring Activity of the Milky Way’s Galactic Center Black Hole in 2019,” Lena Murchikova 2021 ApJL 910 L1. doi:10.3847/2041-8213/abeb70

This publish initially appeared on AAS Nova, which options analysis highlights from the journals of the American Astronomical Society.


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