Artist's impression of a galaxy undergoing a starburst
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Bursts of star birth can curtail future galaxy growth
Astronomers using the NASA/ESA Hubble
Space Telescope have shown for the first time that bursts of star
formation have a major impact far beyond the boundaries of their host
galaxy. These energetic events can affect galactic gas at distances of
up to twenty times greater than the visible size of the galaxy —
altering how the galaxy evolves, and how matter and energy is spread
throughout the Universe.
When galaxies form new stars, they sometimes do so in frantic
episodes of activity known as starbursts. These events were commonplace
in the early Universe, but are rarer in nearby galaxies.
During these bursts, hundreds of millions of stars are born, and
their combined effect can drive a powerful wind that travels out of the
galaxy. These winds were known to affect their host galaxy — but this
new research now shows that they have a significantly greater effect
than previously thought.
An international team of astronomers observed 20 nearby galaxies,
some of which were known to be undergoing a starburst. They found that
the winds accompanying these star formation processes were capable of
ionising [1]
gas up to 650 000 light-years from the galactic centre — around twenty
times further out than the visible size of the galaxy. This is the first
direct observational evidence of local starbursts impacting the bulk of
the gas around their host galaxy, and has important consequences for
how that galaxy continues to evolve and form stars.
“The extended material around galaxies is hard to study, as it’s so faint,” says team member Vivienne Wild of the University of St. Andrews. “But
it’s important — these envelopes of cool gas hold vital clues about how
galaxies grow, process mass and energy, and finally die. We’re
exploring a new frontier in galaxy evolution!”
The team used the Cosmic Origins Spectrograph (COS) instrument [2]
on the NASA/ESA Hubble Space Telescope to analyse light from a mixed
sample of starburst and control galaxies. They were able to probe these
faint envelopes by exploiting even more distant objects — quasars, the
intensely luminous centres of distant galaxies powered by huge black
holes. By analysing the light from these quasars after it passed through
the foreground galaxies, the team could probe the galaxies themselves.
“Hubble is the only observatory that can carry out the observations necessary for a study like this,” says lead author Sanchayeeta Borthakur, of Johns Hopkins University. “We
needed a space-based telescope to probe the hot gas, and the only
instrument capable of measuring the extended envelopes of galaxies is
COS.”
The starburst galaxies within the sample were seen to have large
amounts of highly ionised gas in their halos — but the galaxies that
were not undergoing a starburst did not. The team found that this
ionisation was caused by the energetic winds created alongside newly
forming stars.
This has consequences for the future of the galaxies hosting the
starbursts. Galaxies grow by accreting gas from the space surrounding
them, and converting this gas into stars. As these winds ionise the
future fuel reservoir of gas in the galaxy’s envelope, the availability
of cool gas falls — regulating any future star formation.
“Starbursts are important phenomena — they not only dictate the
future evolution of a single galaxy, but also influence the cycle of
matter and energy in the Universe as a whole,” says team member Timothy Heckman, of Johns Hopkins University. “The
envelopes of galaxies are the interface between galaxies and the rest
of the Universe — and we’re just beginning to fully explore the
processes at work within them.”
The team's results will appear in the 1 May 2013 issue of The Astrophysical Journal.
Notes
[1] A gas is said to be ionised when
its atoms have lost one or more electrons — in this case by energetic
winds exciting galactic gas and knocking electrons out of the atoms
within.
[2] Spectrographs are instruments that break light
into its constituent colours and measure the intensity of each colour,
revealing information about the object emitting the light — such as its
chemical composition, temperature, density, or velocity.
More information
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
The research is presented in a paper entitled “The Impact of
Starbursts on the Circumgalactic Medium”, published in the 1 May 2013
issue of The Astrophysical Journal.
The international team of astronomers in this study consists of: S.
Borthakur (Johns Hopkins University, USA), T. Heckman (Johns Hopkins
University, USA), D. Strickland (Johns Hopkins University, USA), V. Wild
(University of St. Andrews, UK), D. Schiminovich (Columbia University,
USA).
Image credit: ESA, NASA, L. Calçada
Image credit: ESA, NASA, L. Calçada
Links
- Research paper
- Images of Hubble
- Hubble's Instruments: COS — Cosmic Origins Spectrograph
Contacts
Vivienne WildUniversity of St Andrews
UK
Tel: +44 1334 461680
Email: vw8@st-andrews.ac.uk
Sanchayeeta Borthakur
Johns Hopkins University
Baltimore, Md., USA
Tel: +1 410 516 4737
Email: sanch@pha.jhu.edu
Nicky Guttridge
Hubble/ESA
Garching, Germany
Tel: +49-89-3200-6855
Email: nguttrid@partner.eso.org
