New galaxy sheds light on how stars form

Date:
January 25, 2021
Source:
University of Bath
Summary:
Detailed observations of molecular gas in a tidal dwarf galaxy
have important implications for our understanding of how stars
are formed.



FULL STORY ==========================================================================
A lot is known about galaxies. We know, for instance, that the stars
within them are shaped from a blend of old star dust and molecules
suspended in gas.

What remains a mystery, however, is the process that leads to these
simple elements being pulled together to form a new star.


==========================================================================
But now an international team of scientists, including astrophysicists
from the University of Bath in the UK and the National Astronomical
Observatory (OAN) in Madrid, Spain have taken a significant step towards understanding how a galaxy's gaseous content becomes organised into a
new generation of stars.

Their findings have important implications for our understanding of
how stars formed during the early days of the universe, when galaxy
collisions were frequent and dramatic, and star and galaxy formation
occurred more actively than it does now.

For this study, the researchers used the Chile-based Atacama Large
Millimeter Array (ALMA) -- a network of radio telescopes combined to
form one, mega telescope -- to observe a type of galaxy called a tidal
dwarf galaxy (TDG).

TDGs emerge from the debris of two older galaxies colliding with great
force.

They are actively star-forming systems and pristine environments for
scientists trying to piece together the early days of other galaxies,
including our own - - the Milky Way (thought to be 13.6-billion years
old).

"The little galaxy we've been studying was born in a violent, gas-rich
galactic collision and offers us a unique laboratory to study the physics
of star formation in extreme environments," said co-author Professor
Carole Mundell, head of Astrophysics at the University of Bath.

From their observations, the researchers learnt that a TDG's molecular
clouds are similar to those found in the Milky Way, both in terms of
size and content.

This suggests there is a universal star-formation process at play
throughout the universe.



========================================================================== Unexpectedly, however, the TDG in the study (labelled TDG J1023+1952)
also displayed a profusion of dispersed gas. In the Milky Way, clouds
of gas are by far the most prominent star-forming factories.

"The fact that molecular gas appears in both cloud form and as diffuse
gas was a surprise," said Professor Mundell.

Dr Miguel Querejeta from the OAN in Spain and lead author of the study
added: "ALMA's observations were made with great precision so we can say
with confidence that the contribution of diffuse gas is much higher in the tidal dwarf galaxy we studied than typically found in normal galaxies."
He added: "This most likely means most of the molecular gas in this tidal
dwarf galaxy is not involved in forming stars, which questions popular assumptions about star formation." Because of the vast distance that
separates Earth from TDG J1023+1952 (around 50 million light years),
individual clouds of molecular gas appear as tiny regions in the sky when viewed through the naked eye. However, ALMA has the power to distinguish
the smallest details.

"We have managed to identify clouds with an apparent size as small as
observing a coin placed several kilometres away from us," said Professor Mundell, adding: "It's remarkable that we can now study stars and
the gas clouds from which they are formed in a violent extragalactic
collision with the same detail that we can study those forming in the
calm environment of our own Milky Way." The paper ALMA Resolves Giant Molecular Clouds in a Tidal Dwarf Galaxy appears in the latest issue of Astronomy & Astrophysics. This research was a collaborative effort of scientists from across the world working remotely.

Their expertise covers the physics of stars, dust and gas, and the
science of galaxy evolution.


========================================================================== Story Source: Materials provided by University_of_Bath. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. M. Querejeta, F. Lelli, E. Schinnerer, D. Colombo, U. Lisenfeld,
C. G.

Mundell, F. Bigiel, S. Garci'a-Burillo, C. N. Herrera, A. Hughes,
J. M.

D. Kruijssen, S. E. Meidt, T. J. T. Moore, J. Pety,
A. J. Rigby. ALMA resolves giant molecular clouds in a tidal
dwarf galaxy. Astronomy & Astrophysics, 2021; 645: A97 DOI:
10.1051/0004-6361/202038955 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/01/210125113116.htm

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