Has A Mysterious Gamma-Ray Powerhouse Revealed Its Smoking Gun?

Eddie Gonzales Jr. – MessageToEagle.com – In 2016, a binary star system emitting unusually strong gamma-rays was discovered in our galactic neighborhood. Now, astronomers have found the smoking gun —or rather, a smoking trail of cool molecular gas—suggesting the source is jets emanating from a microquasar, one of the few known outside the Milky Way.

Composite optical and X-ray image showing the location of LMC P3 (circled dot) within the DEM L241 supernova remnant. Image credit: Chandra X-ray Observatory Center/NASA’s Goddard Space Flight Center. This image or video was cataloged by Goddard Space Flight Center of the United States National Aeronautics and Space Administration (NASA) under Photo ID: deml241_lmc_p3_circled, Public Domain

Unlike the Milky Way, which shrouds objects behind dust when looking toward the galactic core, the Large Magellanic Cloud (LMC), a dwarf satellite galaxy of our own, offers unhindered views of interesting and relatively nearby astrophysical phenomena.

LMC P3 is one such stellar puzzle. It is the most luminous gamma-ray binary star system, composed of a compact object—either a black hole or a neutron star—alongside a massive star more than 30 times the Sun’s mass. The two stars orbit each other in roughly 10 days.

It lies within the ashes left behind by the supernova that created its compact object. This optically attractive cloud of molecular gas, also known as a supernova remnant, is called DEM L241.

A smoking radio trail

Ever since its discovery, unusually strong gamma-ray emission from LMC P3 has puzzled astronomers. Gamma rays lie at the highest energy limit of the electromagnetic spectrum. But an important clue to LMC P3’s mystery lay at the other end of the spectrum: radio waves.

Starting in 2022, a team led by astronomers from Nagoya University and Gifu University in Japan observed DEM L241/LMC P3 using the ALMA observatory in Chile, one of the world’s largest radio telescopes.

Specifically, they used ALMA bands 6 and 7 to measure carbon monoxide (CO) emission from the surrounding cold molecular gas, at wavelengths around 1.3 mm and 0.87 mm. This helped researchers measure the gas’s structure and motion and estimate its temperature.

What they saw was revealing. “We discovered a gigantic molecular jet,” said Yasuo Fukui, professor emeritus at Nagoya University and lead author of this new discovery, which has been published in The Astrophysical Journal Letters.

The newly discovered jet signature is a strikingly straight and narrow trail of “heated” molecular gas about 26 light-years long and three light-years wide. Although very cold compared to room temperature, this gas trail stands out because it is considerably hotter, at 35 to 60 Kelvin, than the surrounding gas at 15 Kelvin.

Fukui said the relatively high temperature observed across a large fraction of the molecular cloud makes it “a very strong case” that the gas is interacting with a high-energy jet from the compact object—precisely the kind of jet that can also power LMC P3’s gamma rays.

Microquasar mechanism

The new study, which was co-led by Bhuvana Gadikere Rajendra, a researcher, and Kisetsu Tsuge, a designated assistant professor, both at the Institute for Advanced Study at Gifu University, together with Hidetoshi Sano, an associate professor at the Graduate School of Natural Science and Technology at Gifu University, strengthens support for one of two competing theories of gamma-ray binary emission for LMC P3: Microquasar jets.

Previously, pulsar winds were considered a possible mechanism. This scenario requires LMC P3’s compact object to be a pulsar or rapidly spinning neutron star that sends out a wind of energetic particles that collides with its companion star’s stellar wind. This creates a shock wave that accelerates particles to produce gamma rays.

But the newly found jet signature indicates a quasar-like mechanism is the driving process. Quasars are some of the universe’s most luminous objects found in distant galaxies, powered by supermassive black holes at galactic cores accreting material and unleashing powerful jets of matter.

In LMC P3’s case, the compact object could be a stellar-mass black hole or neutron star that draws in material from its companion to form an accretion disk. This is a small-scale version of a quasar, hence termed a microquasar, that can power jets of high-speed particles that can similarly produce gamma rays.

Since black holes drive more powerful jets than neutron stars, the fact that LMC P3’s gamma-ray emission is particularly high “provides a very strong support for the possibility that its central object is a black hole” instead of a neutron star, Fukui said.

Source

Paper

Written by Eddie Gonzales Jr. – MessageToEagle.com Staff Writer