Astronomers using the ALMA observatory have discovered a 26-light-year trail of heated molecular gas in the Large Magellanic Cloud. The finding ties the luminous gamma-ray binary system LMC P3 to microquasar jets, providing strong support for a stellar-mass black hole at its center.
Discovered in 2016, the binary star system known as LMC P3 sits within our galactic neighborhood inside the DEM L241 supernova remnant. Located in the Large Magellanic Cloud, a dwarf satellite galaxy to the Milky Way, the system provides astronomers with an unhindered view free from the dense dust that typically obscures objects toward the center of our own galaxy. LMC P3 ranks as the most luminous gamma-ray binary star system known to science. It pairs a compact object—either a black hole or a neutron star—with a massive companion star more than 30 times heavier than the Sun, completing an orbit roughly every 10 days.
Radio Observations Reveal a Gigantic Molecular Jet in DEM L241
Ever since astronomers first spotted LMC P3, its unusually intense gamma-ray emissions have remained a puzzle. Gamma rays represent the highest energy limit of the electromagnetic spectrum, but researchers found a critical clue at the opposite end of the spectrum using radio telescope observations recorded with the ALMA observatory in Chile starting in 2022.
A research team led by scientists from Nagoya University and Gifu University utilized ALMA bands 6 and 7 to measure carbon monoxide emissions from the surrounding cold molecular gas at wavelengths near 1.3 mm and 0.87 mm. This data allowed the team to map the structure, motion, and temperature of the gas surrounding DEM L241 and LMC P3.
We discovered a gigantic molecular jet.
Yasuo Fukui, professor emeritus at Nagoya University
The newly identified signature takes the form of a straight, narrow trail of molecular gas measuring approximately 26 light-years long and three light-years wide. While extremely cold by everyday standards, the gas stands out against its surroundings by reaching temperatures between 35 and 60 Kelvin, compared to the 15 Kelvin temperature of adjacent gas clouds.
Microquasar Jets Versus Pulsar Winds in LMC P3
The discovery strengthens the case for one of two competing theories regarding how LMC P3 generates its extreme gamma rays. Prior to this study, researchers debated whether the emissions stemmed from pulsar winds or microquasar activity. The pulsar wind scenario requires the compact object to be a rapidly spinning neutron star emitting energetic particle winds that collide with the stellar wind of its companion, generating shock waves that accelerate particles to produce gamma rays.
However, the newly documented jet signature points instead to a quasar-like mechanism operating on a stellar scale. In this model, the compact object pulls material from its massive companion to form an accretion disk, which then powers high-speed particle jets. The research was co-led by Bhuvana Gadikere Rajendra and Kisetsu Tsuge at the Institute for Advanced Study at Gifu University, alongside Hidetoshi Sano at Gifu University’s Graduate School of Natural Science and Technology, with findings published in The Astrophysical Journal Letters.
Implications for the Central Black Hole in the Large Magellanic Cloud
Because stellar-mass black holes generate more powerful jets than neutron stars do, the intensity of the observed jet signature and gamma-ray output carries significant weight for identifying the binary’s hidden engine. The elevated temperature measured across a large fraction of the molecular cloud creates what Fukui described as a very strong case that the gas interacts directly with high-energy jets originating from the compact object.
That interaction, combined with the sheer luminosity of the system’s gamma-ray output, provides a very strong support for the possibility that its central object is a black hole rather than a neutron star, according to the research team.