Artist's Impression of Disk Around a Neutron Star
This illustration shows a neutron star (RX J0806.4-4123) with a disk
of warm dust that produces an infrared signature as detected by NASA’s
Hubble Space Telescope. The disk wasn’t directly photographed, but one
way to explain the data is by hypothesizing a disk structure that could
be 18 billion miles across. The disk would be made up of material
falling back onto the neutron star after the supernova explosion that
created the stellar remnant. Credits: NASA, ESA, and N. Tr’Ehnl (Pennsylvania State University). Release Images
An unusual infrared light emission from a nearby neutron star
detected by NASA’s Hubble Space Telescope, could indicate new features
never before seen. One possibility is that there is a dusty disk
surrounding the neutron star; another is that there is an energetic wind
coming off the object and slamming into gas in interstellar space the
neutron star is plowing through.
Although neutron stars are generally studied in radio and high-energy
emissions, such as X-rays, this study demonstrates that new and
interesting information about neutron stars can also be gained by
studying them in infrared light, say researchers.
The observation, by a team of researchers at Pennsylvania State
University, University Park, Pennsylvania; Sabanci University, Istanbul,
Turkey; and the University of Arizona, Tucson, Arizona could help
astronomers better understand the evolution of neutron stars — the
incredibly dense remnants after a massive star explodes as a supernova.
Neutron stars are also called pulsars because their very fast rotation
(typically fractions of a second, in this case 11 seconds) causes
time-variable emission from light-emitting regions.
A paper describing the research and two possible explanations for the unusual finding appears Sept. 17, 2018 in the Astrophysical Journal.
“This particular neutron star belongs to a group of seven nearby
X-ray pulsars — nicknamed ‘the Magnificent Seven’ — that are hotter than
they ought to be considering their ages and available energy reservoir
provided by the loss of rotation energy,” said Bettina Posselt,
associate research professor of astronomy and astrophysics at
Pennsylvania State and the lead author of the paper. “We observed an
extended area of infrared emissions around this neutron star — named RX
J0806.4-4123 — the total size of which translates into about 200
astronomical units (approximately 18 billion miles) at the assumed
distance of the pulsar.”
This is the first neutron star in which an extended signal has been
seen only in infrared light. The researchers suggest two possibilities
that could explain the extended infrared signal seen by the Hubble. The
first is that there is a disk of material — possibly mostly dust —
surrounding the pulsar.
“One theory is that there could be what is known as a ‘fallback disk’
of material that coalesced around the neutron star after the
supernova,” said Posselt. “Such a disk would be composed of matter from
the progenitor massive star. Its subsequent interaction with the neutron
star could have heated the pulsar and slowed its rotation. If confirmed
as a supernova fallback disk, this result could change our general
understanding of neutron star evolution.”
The second possible explanation for the extended infrared emission from this neutron star is a “pulsar wind nebula.”
“A pulsar wind nebula would require that the neutron star exhibits a
pulsar wind,” said Posselt. “A pulsar wind can be produced when
particles are accelerated in the electrical field that is produced by
the fast rotation of a neutron star with a strong magnetic field. As the
neutron star travels through the interstellar medium at greater than
the speed of sound, a shock can form where the interstellar medium and
the pulsar wind interact. The shocked particles would then emit
synchrotron radiation, causing the extended infrared signal that we see.
Typically, pulsar wind nebulae are seen in X-rays and an infrared-only
pulsar wind nebula would be very unusual and exciting.”
Using NASA’s upcoming James Webb Space Telescope, astronomers will be
able to further explore this newly opened discovery space in the
infrared to better understand neutron star evolution.
In addition to Posselt, the research team included George Pavlov and
Kevin Luhman at Pennsylvania State; Ünal Ertan and Sirin Çaliskan at
Sabanci University; and Christina Williams at the University of Arizona.
The research was supported by NASA, The Scientific and Technological
Research Council of Turkey, the U.S. National Science Foundation,
Pennsylvania State, the Penn State Eberly College of Science, and the
Pennsylvania Space Grant Consortium.
The Hubble Space Telescope is a project of international cooperation
between NASA and ESA (European Space Agency). NASA's Goddard Space
Flight Center in Greenbelt, Maryland, manages the telescope. The Space
Telescope Science Institute (STScI) in Baltimore, Maryland, conducts
Hubble science operations. STScI is operated for NASA by the Association
of Universities for Research in Astronomy, in Washington, D.C.
Related Links
Related Links
This site is not responsible for content found on external links
Contact
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu
Dr. Samuel J. Sholtis
Penn State Eberly College of Science, Office of Communications, University Park, Pennsylvania
814-865-1390
samsholtis@psu.edu
