The Atacama Large Millimeter/submillimeter Array (ALMA) has revealed the telltale signs of 11 low-mass stars forming close – within just 3 light-years — to Sagittarius A*, a supermassive black hole at the center of our Milky Way Galaxy.
An ALMA image of the center of the Milky Way Galaxy showing the location of 11 young protostars within about 3 light-years of Sagittarius A*. The lines indicate the direction of the bipolar lobes created by high-velocity jets from the protostars. The illustrated star in the middle of the image indicates the location of Sagittarius A*. Image credit: ALMA / Yusef-Zadeh et al / B. Saxton / ESO / NAOJ / NRAO / AUI / NSF.
The Milky Way’s Galactic center, with its 4 million solar mass black hole Sagittarius A*, is located approximately 26,000 light-years from Earth in the direction of the constellation Sagittarius.
Vast stores of interstellar dust obscure this region, hiding it from optical telescopes. Radio waves, including the millimeter and submillimeter light that ALMA sees, are able to penetrate this dust, giving astronomers a clearer picture of the dynamics and content of this hostile environment.
Prior ALMA observations of the region surrounding Sagittarius A* revealed multiple young stars that are estimated to be about 6 million years old. These objects, known as proplyds, are common features in more placid star-forming regions, like the Orion Nebula.
The new ALMA observations, however, revealed something even more remarkable, signs that eleven low-mass protostars are forming within 3 light-years of Sagittarius A*.
The presence of these protostars suggests that the conditions necessary to birth low-mass stars may exist even in one of the most turbulent regions of the Milky Way and possibly in similar locales throughout the Universe.
“Despite all odds, we see the best evidence yet that low-mass stars are forming startlingly close to Sagittarius A*,” said Dr. Farhad Yusef-Zadeh, an astronomer at Northwestern University.
“This is a genuinely surprising result and one that demonstrates just how robust star formation can be, even in the most unlikely of places.”
The ALMA data also suggest that the newly-discovered protostars are about 6,000 years old.
“This is important because it is the earliest phase of star formation we have found in this highly hostile environment,” Dr. Yusef-Zadeh said.
In this artist’s conception of an infant solar system, the young star pulls material from its surroundings into a rotating disk (right) and generates outflowing jets of material (left). Image credit: Bill Saxton / NRAO / AUI / NSF.
The researchers identified these protostars by seeing the classic ‘double lobes’ of material that bracket each of them. These cosmic hourglass-like shapes signal the early stages of star formation. Molecules, like carbon monoxide, in these lobes glow brightly in millimeter-wavelength light, which ALMA can observe with remarkable precision and sensitivity.
“This discovery provides evidence that star formation is taking place within clouds surprisingly close to Sagittarius A*,” said Dr. Al Wootten, from the National Radio Astronomy Observatory.
“Though these conditions are far from ideal, we can envision several pathways for these stars to emerge.”
For this to occur, outside forces would have to compress the gas clouds near the center of our Galaxy to overcome the violent nature of the region and allow gravity to take over and form stars.
The scientists speculate that high-velocity gas clouds could aid in star formation as they force their way through the interstellar medium.
It is also possible that jets from Sagittarius A* itself could be plowing into the surrounding gas clouds, compressing material and triggering this burst of star formation.
“The next step is to take a closer look to confirm that these newly formed stars are orbited by disks of dusty gas,” said Dr. Mark Wardle, an astronomer at Macquarie University in Sydney, Australia.
“If so, it’s likely that planets will eventually form from this material, as is the case for young stars in the galactic disk.”
A paper reporting this discovery is published in the Astrophysical Journal Letters.
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F. Yusef-Zadeh et al. 2017. ALMA Detection of Bipolar Outflows: Evidence for Low-mass Star Formation within 1 pc of Sgr A*. ApJL 850, L30; doi: 10.3847/2041-8213/aa96a2
