NGC 602
Credit : X-ray: NASA/CXC/Univ.Potsdam/L.Oskinova et al;
Optical: NASA/STScI;
Infrared: NASA/JPL-Caltech
The Small Magellanic Cloud (SMC) is one of the Milky Way's closest galactic neighbors. Even though it is a small, or so-called dwarf galaxy, the SMC is so bright that it is visible to the unaided eye from the Southern Hemisphere and near the equator. Many navigators, including Ferdinand Magellan who lends his name to the SMC, used it to help find their way across the oceans.
Modern astronomers are also interested in studying the SMC (and its cousin, the Large Magellanic Cloud),
but for very different reasons. Because the SMC is so close and
bright, it offers an opportunity to study phenomena that are difficult
to examine in more distant galaxies.
New Chandra data of the SMC have provided one such discovery: the first detection of X-ray emission from young stars with masses similar to our Sun
outside our Milky Way galaxy. The new Chandra observations of these
low-mass stars were made of the region known as the "Wing" of the SMC.
In this composite image of the Wing the Chandra data is shown in purple,
optical data from the Hubble Space Telescope is shown in red, green and
blue and infrared data from the Spitzer Space Telescope is shown in
red.
Astronomers call all elements heavier than hydrogen and helium
- that is, with more than two protons in the atom's nucleus - "metals."
The Wing is a region known to have fewer metals compared to most
areas within the Milky Way. There are also relatively lower amounts of
gas, dust, and stars in the Wing compared to the Milky Way.
Taken together, these properties make the Wing an excellent location to study the life cycle of stars
and the gas lying in between them. Not only are these conditions
typical for dwarf irregular galaxies like the SMC, they also mimic ones
that would have existed in the early Universe.
Most star formation near the tip of the Wing is occurring in a small
region known as NGC 602, which contains a collection of at least three
star clusters. One of them, NGC 602a, is similar in age, mass, and size
to the famous Orion Nebula
Cluster. Researchers have studied NGC 602a to see if young stars - that
is, those only a few million years old - have different properties when
they have low levels of metals, like the ones found in NGC 602a.
Using Chandra, astronomers discovered extended X-ray emission, from
the two most densely populated regions in NGC 602a. The extended X-ray
cloud likely comes from the population of young, low-mass stars in the
cluster, which have previously been picked out by infrared and optical
surveys, using Spitzer and Hubble respectively. This emission is not
likely to be hot gas blown away by massive stars, because the low metal
content of stars in NGC 602a implies that these stars should have weak
winds. The failure to detect X-ray emission from the most massive star
in NGC 602a supports this conclusion, because X-ray emission is an
indicator of the strength of winds from massive stars. No individual
low-mass stars are detected, but the overlapping emission from several
thousand stars is bright enough to be observed.
The Chandra results imply that the young, metal-poor stars in NGC
602a produce X-rays in a manner similar to stars with much higher metal
content found in the Orion cluster in our galaxy. The authors speculate
that if the X-ray properties of young stars are similar in different
environments, then other related properties -- including the formation
and evolution of disks where planets form -- are also likely to be
similar.
X-ray emission traces the magnetic activity of young stars and is
related to how efficiently their magnetic dynamo operates. Magnetic
dynamos generate magnetic fields in stars through a process involving
the star's speed of rotation, and convection, the rising and falling of
hot gas in the star's interior.
The combined X-ray, optical and infrared data also revealed, for the
first time outside our Galaxy, objects representative of an even younger
stage of evolution of a star. These so-called “young stellar
objects†have ages of a few thousand years and are still embedded in
the pillar of dust and gas from which stars form, as in the famous "Pillars of Creation" of the Eagle Nebula. A labeled version shows the location of these young stellar objects (roll your mouse over the image above).
A paper describing these results was published online
and in the March 1, 2013 issue of The Astrophysical Journal. The first
author is Lidia Oskinova from the University of Potsdam in Germany and
the co-authors are Wei Sun from Nanjing University, China; Chris Evans
from the Royal Observatory Edinburgh, UK; Vincent Hénault-Brunet from
University of Edinburgh, UK; You-Hua Chu from the University of
Illinois, Urbana, IL; John Gallagher III from the University of
Wisconsin-Madison, Madison, WI; Martin Guerrero from the Instituto de
Astrofísica de Andalucía, Spain; Robert Gruendl from the University of
Illinois, Urbana, IL; Manuel Güdel from the University of Vienna,
Austria; Sergey Silich from the Instituto Nacional de Astrofísica Optica
y Electrónica, Puebla, Mexico; Yang Chen from Nanjing University,
China; Yael Nazé from Université de Liège, Liège, Belgium; Rainer
Hainich from the University of Potsdam, Germany, and Jorge
Reyes-Iturbide from the Universidade Estadual de Santa Cruz, Ilhéus,
Brazil.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the
Chandra program for NASA's Science Mission Directorate in Washington.
The Smithsonian Astrophysical Observatory controls Chandra's science and
flight operations from Cambridge, Mass.
Scale: Image is 3 arcmin across (160 light years)
Category: Normal Stars & Star Clusters
Coordinates (J2000): RA 01h 29m 12.40s | Dec -73° 32' 01.70"
Constellation: Hydrus
Observation Date: 11 pointings between 31 March and 29 April, 2010
Observation Time: 80 hours 45 min (3 days 8 hours 45 min)
Obs. ID: 10985-10986, 11978-11979, 11988-11989, 12130-12131, 12134, 12136, 12207
Instrument: ACIS
References: Oskinova, L. et al, 2013, ApJ, 765 73; arXiv:1301.3500
Color Code: X-ray (Purple); Optical (Red, Green, Blue); Infrared (Red)
