10 research outputs found
A runaway collision in a young star cluster as the origin of the brightest supernova
Supernova 2006gy in the galaxy NGC 1260 is the most luminous one recorded
\cite{2006CBET..644....1Q, 2006CBET..647....1H, 2006CBET..648....1P,
2006CBET..695....1F}. Its progenitor might have been a very massive (
\msun) star \cite{2006astro.ph.12617S}, but that is incompatible with hydrogen
in the spectrum of the supernova, because stars \msun are believed to
have shed their hydrogen envelopes several hundred thousand years before the
explosion \cite{2005A&A...429..581M}. Alternatively, the progenitor might have
arisen from the merger of two massive stars \cite{2007ApJ...659L..13O}. Here we
show that the collision frequency of massive stars in a dense and young cluster
(of the kind to be expected near the center of a galaxy) is sufficient to
provide a reasonable chance that SN 2006gy resulted from such a bombardment. If
this is the correct explanation, then we predict that when the supernova fades
(in a year or so) a dense cluster of massive stars becomes visible at the site
of the explosion
An upper limit to the masses of stars
There is no accepted upper mass limit for stars. Such a basic quantity
escapes both theory, because of incomplete understanding of star formation, and
observation, because of incompleteness in surveying the Galaxy. The Arches
cluster is ideal for such a test, being massive enough to expect stars at least
as massive as 400 solar masses, and young enough for its most massive members
to still be visible. It is old enough to be free of its natal molecular cloud,
and close enough, and at a well-established distance, for us to discern its
individual stars. Here I report an absence of stars with initial masses greater
than 130 M_Sun in the Arches cluster, where the typical mass function predicts
18. I conclude that this indicates a firm limit of 150 M_Sun for stars as the
probability that the observations are consistent with no limit is 10^-8.Comment: To appear in Nature, March 10, 2005, Vol. 34, No. 7030, 192 (ST ScI
Eprint #1645). More files can be found at http://www.stsci.edu/~fige
The Initial Mass Function in the Galactic Center
The Galactic Center contains the most massive young clusters in the Galaxy
and serves as the closest example of a massive starburst region. Our recent
results suggest that the Galactic Center environment produces massive clusters
with relatively flat initial mass functions, as might be expected on
theoretical grounds. I will discuss these recent results, along with evidence
for star formation in the immediate vicinity of the super massive black hole at
the Galactic Center. The results of this work might be useful in extrapolating
to other galactic centers with similar conditions, as well as other starburst
regions