NASA's Nuclear Spectroscope Telescope Array, or NuSTAR, has identified a
candidate pulsar in Andromeda -- the nearest large galaxy to the Milky
Way. This likely pulsar is brighter at high energies than the Andromeda
galaxy's entire black hole population. Image credit:
NASA/JPL-Caltech/GSFC/JHU . › Full image and caption
The Milky Way's close neighbor, Andromeda, features a dominant source
of high-energy X-ray emission, but its identity was mysterious until
now. As reported in a new study, NASA's NuSTAR (Nuclear Spectroscopic
Telescope Array) mission has pinpointed an object responsible for this
high-energy radiation.
The object, called Swift J0042.6+4112, is a possible pulsar, the
dense remnant of a dead star that is highly magnetized and spinning,
researchers say. This interpretation is based on its emission in
high-energy X-rays, which NuSTAR is uniquely capable of measuring. The
object's spectrum is very similar to known pulsars in the Milky Way.
It is likely in a binary system, in which material from a stellar
companion gets pulled onto the pulsar, spewing high-energy radiation as
the material heats up.
"We didn't know what it was until we looked at it with NuSTAR," said
Mihoko Yukita, lead author of a study about the object, based at Johns
Hopkins University in Baltimore. The study is published in The
Astrophysical Journal.
This candidate pulsar is shown as a blue dot in a NuSTAR X-ray image
of Andromeda (also called M31), where the color blue is chosen to
represent the highest-energy X-rays. It appears brighter in high-energy
X-rays than anything else in the galaxy.
The study brings together many different observations of the object
from various spacecraft. In 2013, NASA's Swift satellite reported it as a
high-energy source, but its classification was unknown, as there are
many objects emitting low energy X-rays in the region. The lower-energy
X-ray emission from the object turns out to be a source first identified
in the 1970s by NASA's Einstein Observatory.
Other spacecraft, such as
NASA's Chandra X-ray Observatory and ESA's XMM-Newton had also detected
it. However, it wasn't until the new study by NuSTAR, aided by
supporting Swift satellite data, that researchers realized it was the
same object as this likely pulsar that dominates the high energy X-ray
light of Andromeda.
Traditionally, astronomers have thought that actively feeding black
holes, which are more massive than pulsars, usually dominate the
high-energy X-ray light in galaxies. As gas spirals closer and closer to
the black hole in a structure called an accretion disk, this material
gets heated to extremely high temperatures and gives off high-energy
radiation. This pulsar, which has a lower mass than any of Andromeda's
black holes, is brighter at high energies than the galaxy's entire black
hole population.
Even the supermassive black hole in the center of Andromeda does not
have significant high-energy X-ray emission associated with it. It is
unexpected that a single pulsar would instead be dominating the galaxy
in high-energy X-ray light.
"NuSTAR has made us realize the general importance of pulsar systems
as X-ray-emitting components of galaxies, and the possibility that the
high energy X-ray light of Andromeda is dominated by a single pulsar
system only adds to this emerging picture," said Ann Hornschemeier,
co-author of the study and based at NASA's Goddard Space Flight Center,
Greenbelt, Maryland.
Andromeda is a spiral galaxy slightly larger than the Milky Way. It
resides 2.5 million light-years from our own galaxy, which is considered
very close, given the broader scale of the universe. Stargazers can see
Andromeda without a telescope on dark, clear nights.
"Since we can't get outside our galaxy and study it in an unbiased
way, Andromeda is the closest thing we have to looking in a mirror,"
Hornschemeier said.
NuSTAR is a Small Explorer mission led by Caltech and managed by JPL
for NASA's Science Mission Directorate in Washington. NuSTAR was
developed in partnership with the Danish Technical University and the
Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences
Corp., Dulles, Virginia. NuSTAR's mission operations center is at UC
Berkeley, and the official data archive is at NASA's High Energy
Astrophysics Science Archive Research Center. ASI provides the mission's
ground station and a mirror archive. JPL is managed by Caltech for
NASA.
News Media Contact
Elizabeth Landau
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6425
elizabeth.landau@jpl.nasa.gov
Source: JPL-Caltech
