By Heather Hamilton, contributing writer
Pulsars, the dense, spinning cores of collapsed stars up to 30 times larger than the sun, are the most likely cause for the gamma-ray glow at the center of the Milky Way, according to an international team of astrophysicists, which contains researchers from the Department of Energy’s SLAC National Accelerator Laboratory. This directly contradicts earlier ideas that the glow was a sign of dark matter, which accounts for 85% of all matter in the universe but has yet to be detected, a SLAC press release says.
While little is known about dark matter, researchers know that it exists because of the bending of light from faraway galaxies, as well as their rotation. The general consensus is that dark matter is composed of particles that are yet to be discovered.
Mattia Di Mauro, from the Kavli Institute for Particle Astrophysics and Cosmology (a joint institute of Stanford University and SLAC), says that the study shows that dark matter is not necessary to understanding the gamma-ray emissions without our galaxy. “Instead, we have identified a population of pulsars in the region around the galactic center, which sheds new light on the formation history of the Milky Way.”
Di Mauro held a leadership role for the Fermi LAT Collaboration, which looked at the glow with the Large Area Telescope on NASA’s Fermi Gamma-ray Space Telescope, orbiting Earth since 2008. The telescope, which can see gamma rays, was invented and assembled at SLAC. Results of the collaboration can be read in preprint and will likely be printed in The Astrophysical Journal.
Researchers found the speckled gamma-ray signal to be consistent with pulsars. “Considering that about 70% of all point sources in the Milky Way are pulsars, they were the most likely candidates. But we used one of their physical properties to come to our conclusion. Pulsars have very distinct spectra — that is, their emissions vary in a specific way with the energy of the gamma rays they emit. Using the shape of these spectra, we were able to model the glow of the galactic center correctly with a population of about 1,000 pulsars and without introducing processes that involve dark matter particles,” Di Mauro said.
In an interview with Gizmodo, Di Mauro revealed that researchers made a list of 400 objects in the center of the galaxy to determine what could be contributing to the gamma glow. They then cut the list to a possible 66 pulsars and put the data in for computer simulation, which accounted for the excess radiation.
“From our findings, there should be this population of pulsars in the galactic bulge around the galactic center,” Di Mauro told Gizmodo. “These should explain the [excess] energy.”
Radio telescopes will now be used by the team to find out more information about the light source, including whether or not the glow results from brief light pulses, from which pulsars receive their name. Researchers hope that further investigation will lend them details about history being that discoveries in the stars at the center of the galaxy, which is the oldest part of the Milky Way, reveal information about the galaxy’s evolution.
“Isolated pulsars have a typical lifetime of 10 million years, which is much shorter than the age of the oldest stars near the galactic center,” said KIPAC’s Eric Charles. “The fact that we can still see gamma rays from the identified pulsar population today suggests that the pulsars are in binary systems with companion stars from which they leach energy. This extends the life of the pulsars tremendously.”
If the light signals consisted of dark matter, researchers could expect to see similar effects at the centers of other galaxies, particularly in dwarf galaxies that orbit the Milky Way. They have fewer stars, which means fewer pulsars — though they’re also not emitting gamma rays, either. The Andromeda galaxy, which is the closest major galaxy, is also emitting a strong gamma-ray glow, which may be the work of pulsars.
While the research is promising, it has not yet been peer-reviewed.
Sources: SLAC, Arxiv.org, Gizmodo
Image Source: Wikimedia
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