Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered that two young stars forming from the same swirling protoplanetary disk may be twins — in the sense that they came from the same parent cloud of star-forming material. Beyond that, however, they have shockingly little in common.
The main, central star of this system, which is located approximately
11,000 light-years from Earth, is truly colossal — a full 40 times more
massive than the Sun. The other star, which ALMA recently discovered
just beyond the central star’s disk, is a relatively puny one-eightieth
(1/80) that mass.
Their striking difference in size suggests that they formed by
following two very different paths. The more massive star took the more
traditional route by collapsing under gravity out of a dense “core” of
gas. The smaller one likely followed the road less traveled by – at
least for stars – by accumulating mass from a portion of the disk that
“fragmented” away as it matured, a process that may have more in common
with the birth of gas-giant planets.
“Astronomers have known for a long time that most massive stars orbit
one or more other stars as partners in a compact system, but how they
got there has been a topic of conjecture,” said Crystal Brogan, an
astronomer with the National Radio Astronomy Observatory (NRAO) in
Charlottesville, Virginia, and a co-author on the study. “With ALMA, we
now have evidence that the disk of gas and dust that encompasses and
feeds a growing massive star also produces fragments at early stages
that can form a secondary star.”
The main object, known as MM 1a, is a previously identified young
massive star surrounded by a rotating disk of gas and dust. A faint
protostellar companion to this object, MM 1b, was newly detected by ALMA
just outside the MM 1a protoplanetary disk. The team believes this is
one of the first examples of a fragmented disk to be detected around a
massive young star.
“This ALMA observation opens new questions, such as ‘Does the
secondary star also have a disk?’ and ‘How fast can the secondary star
grow?’ The amazing thing about ALMA is that we have not yet used its
full capabilities in this area, which will someday allow us to answer
these new questions,” said co-author Todd Hunter, who is also with the
NRAO in Charlottesville.
Stars form within large clouds of gas and dust in interstellar space.
When these clouds collapse under gravity, they begin to rotate faster,
forming a disk around them.
“In low-mass stars like our Sun, it is in these disks that planets
can form,” said John Ilee, an astronomer at Leeds University in England
and lead author on the study. “In this case, the star and disk we have
observed are so massive that, rather than witnessing a planet forming in
the disk, we are seeing another star being born.”
By observing the millimeter wavelength light naturally emitted by the
dust, and subtle shifts in the frequency of light emitted by the gas,
the researchers were able to calculate the mass of MM 1a and MM 1b.
Their work is published in the Astrophysical Journal Letters.
“Many older massive stars are found with nearby companions,” added
Ilee. “But binary stars are often very equal in mass, and so likely
formed together as siblings. Finding a young binary system with a mass
ratio of 80-to-1 is very unusual and suggests an entirely different
formation process for both objects.”
The favored formation process for MM 1b occurs in the outer regions
of cold, massive disks. These “gravitationally unstable” disks are
unable to hold themselves up against the pull of their own gravity,
collapsing into one – or more – fragments.
The researchers note that newly discovered young star MM 1b could
also be surrounded by its own circumstellar disk, which may have the
potential to form planets of its own – but it will need to be quick.
“Stars as massive as MM 1a only live for around a million years before
exploding as powerful supernovae, so while MM 1b may have the potential
to form its own planetary system in the future, it won’t be around for
long,” Ilee concluded.
Additional Information
This research was published in the Astrophysical Journal Letters in an article titled “G11.92–0.61 MM 1: A Fragmented Keplerian Disk Surrounding a Proto-O Star” by J. D. Ilee.
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of the European
Southern Observatory (ESO), the U.S. National Science Foundation (NSF)
and the National Institutes of Natural Sciences (NINS) of Japan in
cooperation with the Republic of Chile. ALMA is funded by ESO on behalf
of its Member States, by NSF in cooperation with the National Research
Council of Canada (NRC) and the Ministry of Science and Technology
(MOST) in Taiwan and by NINS in cooperation with the Academia Sinica
(AS) in Taiwan and the Korea Astronomy and Space Science Institute
(KASI).
ALMA construction and operations are led by ESO on behalf of its
Member States; by the National Radio Astronomy Observatory (NRAO),
managed by Associated Universities, Inc. (AUI), on behalf of North
America; and by the National Astronomical Observatory of Japan (NAOJ) on
behalf of East Asia. The Joint ALMA Observatory (JAO) provides the
unified leadership and management of the construction, commissioning and
operation of ALMA.
Contacts
Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
Email: nicolas.lira@alma.cl
Charles E. Blue
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia - USA
Phone: +1 434 296 0314
Cell phone: +1 202 236 6324
Email: cblue@nrao.edu
Calum Turner
ESO Assistant Public Information Officer
Garching bei München, Germany
Phone: +49 89 3200 6670
Email: calum.turner@eso.org
Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory , Tokyo - Japan
Phone: +81 422 34 3630
Contacts
Nicolás Lira
Education and Public Outreach Coordinator
Joint ALMA Observatory, Santiago - Chile
Phone: +56 2 2467 6519
Cell phone: +56 9 9445 7726
Email: nicolas.lira@alma.cl
Charles E. Blue
Public Information Officer
National Radio Astronomy Observatory Charlottesville, Virginia - USA
Phone: +1 434 296 0314
Cell phone: +1 202 236 6324
Email: cblue@nrao.edu
Calum Turner
ESO Assistant Public Information Officer
Garching bei München, Germany
Phone: +49 89 3200 6670
Email: calum.turner@eso.org
Masaaki Hiramatsu
Education and Public Outreach Officer, NAOJ Chile
Observatory , Tokyo - Japan
Phone: +81 422 34 3630
