Explosive birth of stars swells galactic cores

Submillimeter waves detected with ALMA are shown in the
left, indicating the location of dense dust and gas where stars
are being formed. Optical and infrared light seen with the
Hubble Space Telescope are shown in the middle and right,
respectively. A large galactic disk is seen in infrared, while
three young star clusters are seen in optical light. Credit:
ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, Tadaki
et al.

Astronomers found that active star formation upswells
galaxies, like yeast helps bread rise. Using three powerful
telescopes on the ground and in orbit, they observed galaxies
from 11 billion years ago and found explosive formation of
stars in the cores of galaxies. This suggests that galaxies
can change their own shape without interaction with other
galaxies.

“Massive elliptical galaxies are believed to be formed from
collisions of disk galaxies,” said Ken-ichi Tadaki, the lead
author of two research papers and a postdoctoral researcher at
the National Astronomical Observatory of Japan (NAOJ). “But, it
is uncertain whether all the have experienced galaxy
collision. There may be an alternative path.”

Aiming to understand galactic metamorphosis, the international
team explored distant galaxies 11 billion light-years away.
Because it takes time for the light from distant objects to
reach us, by observing galaxies 11 billion light-years away,
the team can see what the Universe looked like 11 billion years
ago, 3 billion years after the Big Bang. This corresponds the
peak epoch of galaxy formation; the foundations of most
galaxies were formed in this epoch.

Receiving faint light which has travelled 11 billion years is
tough work. The team harnessed the power of three telescopes to
anatomize the ancient galaxies. First, they used NAOJ’s 8.2-m
Subaru Telescope in Hawai`i and picked out 25 galaxies in this
epoch. Then they targeted the galaxies for observations with
NASA/ESA’s Hubble Space Telescope (HST) and the Atacama Large
Millimeter/submillimeter Array (ALMA). The astronomers used HST
to capture the light from which tells us the “current” (as of when
the light was emitted, 11 billion years ago) shape of the
galaxies, while ALMA observed submillimeter waves from cold
clouds of gas and dust, where new stars are being formed. By
combining the two, we know the shapes of the galaxies 11
billion years ago and how they are evolving.

Stars are actively formed in the massive reservoir of dust
and gas at the center of the galaxy. Credit: NAOJ

Thanks to their high resolution, HST and ALMA could illustrate
the metamorphosis of the galaxies. With HST images the team
found that a disk component dominates the galaxies. Meanwhile,
the ALMA images show that there is a massive reservoir of gas
and dust, the material of stars, so that stars are forming very
actively. The star formation activity is so high that huge
numbers of stars will be formed at the centers of the galaxies.
This leads the astronomers to think that ultimately the
galaxies will be dominated by the stellar bulge and become
elliptical or lenticular galaxies.

“Here, we obtained firm evidence that dense galactic cores can
be formed without galaxy collisions. They can also be formed by
intense in the heart of the
galaxy.” said Tadaki. The team used the European Southern
Observatory’s Very Large Telescope to observe the target
galaxies and confirmed that there are no indications of massive
galaxy collisions.

First the galaxy is dominated by the disk component (left)
but active star formation occurs in the huge dust and gas cloud
at the center of the galaxy (center). Then the galaxy is
dominated by the stellar bulge and becomes an elliptical or
lenticular galaxy. Credit: NAOJ

Almost 100 years ago, American Edwin Hubble invented the
morphological classification scheme for galaxies. Since then,
many astronomers have devoted considerable effort to
understanding the origin of the variety in galaxy shapes.
Utilizing the most advanced telescopes, modern astronomers have
come one step closer to solving the mysteries of .

Explore further:

Running out of gas: Gas loss puts breaks on stellar baby
boom

More information: Ken-ichi Tadaki et al, Rotating
starburst cores in massive galaxies at z = 2.5, The
Astrophysical Journal
(2017). DOI: 10.3847/2041-8213/aa7338

Ken-ichi Tadaki et al. Bulge-forming galaxies with an extended
rotating disk at z∼ 2, The Astrophysical Journal (2017).

DOI: 10.3847/1538-4357/834/2/135

Journal reference: Astrophysical
Journal

Provided by: National Institutes of Natural Sciences