Astronomers have discovered a cosmic flash that originated 5 billion years ago. It is the most remote megamaser ever observed and reveals that a collision of galaxies occurred when the universe was a third of its current age.
Using the South African MeerKAT radio telescope, an international team of researchers has discovered a powerful megamaser: a radio wavelength laser indicative of colliding galaxies. This is the most distant megamaser found so far.
Galaxies are vast islands of matter in the universe. They contain hundreds of billions of stars, gas and dark matter. When galaxies merge in collisions of cosmic proportions, the gas they contain becomes extremely dense.
At that time, the gas can stimulate the hydroxyl molecules, composed of one oxygen atom and one hydrogen atom, to emit a specific radio signal called maser (A maser is like a laser, but it emits radio waves instead of visible light.) When that radio signal is extremely bright, it’s called a megamaser.
“When two galaxies, such as the Milky Way and the Andromeda Galaxy, collide, light rays shoot out from the collision and can be seen at cosmological distances. Hydroxyl (OH) megamasers act like bright lights that indicate: here is a colliding galaxy that is forming new stars and fueling massive black holes”, explains Jeremy Darling, from the University of Colorado and co-author of the study.
Hydroxyl megamasers emit light at a wavelength of 18 cm. This light belongs to the radio part of the electromagnetic spectrum, and it’s the kind of light that the MeerKAT radio telescope is designed to pick up exceptionally well, the researchers note.
The LADUMA team (Looking at the Distant Universe with the Meerkat Array) leads one of MeerKAT’s great scientific experiments, which searches for neutral hydrogen gas in galaxies located in an area of the sky, and searches for it very deep, that is, very far from us, both in space and in time.
By measuring neutral hydrogen gas in galaxies from the distant past until now, LADUMA contributes to our understanding of the evolution of the universe.
It is not a minor exercise, so the research team is made up of scientists from South Africa, Australia, Chile, France, Germany, India, Italy, Japan, the Netherlands, South Korea, Spain (Institute of Astrophysics of Andalusia), United Kingdom and United States.
“LADUMA is investigating hydrogen within a single ‘vuvuzela or cosmic trumpet’ that stretches back to when the universe was only a third of its current age,” says Associate Professor Sarah Blyth of the University of Cape Town.
To search for hydrogen, the team probes light with a wavelength of 21 cm, which has been stretched to longer wavelengths due to the expansion of the universe.
However, light from other atoms and molecules is also present, and in their first observation with MeerKAT, the team detected bright emission from hydroxyl molecules that had been further stretched from their original wavelength of 18 cm.
The director of this investigation, Marcin Glowacki, from the International Center for Radio Astronomy Research (ICRAR), explains that “it is impressive that in a single night of observations with MeerKAT, we have already found a record-breaking redshift megamaser. The full LADUMA survey of over 3,000 hours will be the most sensitive of its kind.”
When they saw this signal in the data from the telescope and confirmed that it came from hydroxyl, the team realized they had a megamaser on their hands.
To make this discovery, the team had to run complex scientific algorithms on large amounts of data. This was possible thanks to the cloud computing capacity of the Interuniversity Institute for Data Intensive Astronomy (IDIA).
Once the team learned that it was a megamaser, they proceeded to search for its host galaxy. The portion of the sky explored by the LADUMA team has been observed in X-rays, optical light, and infrared, so the team was able to easily identify the host galaxy.
The team also knew that such a powerful and aloof megamaser needed a good nickname and invited suggestions from the public.
The winning entry was “Nkalakatha”, an isiZulu word meaning “big boss”, which was suggested by Zolile Tibane, a student from Johannesburg studying computer science at the University of the Western Cape.
The host galaxy of “Nkalakatha” is known to have a long tail on one side, visible in radio waves. It is about 58 followed by 21 zeros of kilometers away from Earth, and the light from the megamaser was emitted about 5 billion years agowhen the universe was only two-thirds its current age.
“We have already planned follow-up observations of the megamaser, and as LADUMA progresses we will make many more discoveries,” says Glowacki.
“MeerKAT will likely double the known number of these rare phenomena. Galaxies were thought to merge more frequently in the past, and the recently discovered OH megamasers will allow us to test this hypothesis,” says Darling.
SARAO at the forefront
Radio astronomy is entering a really exciting time with the upcoming Square Kilometer Array and its pioneering telescopes, including MeerKAT, the researchers say.
Unplanned discoveries are beginning to emerge from the unprecedented amount of data these instruments collect.
The South African Radio Astronomy Observatory (SARAO) leads South Africa’s activities on the Square Kilometer Array radio telescope, commonly known as the SKA, in engineering, science and construction. It incorporates radio astronomy instruments and programs such as the MeerKAT telescope that has detected the most distant megamaser to date.
LADUMA: Discovery of a luminous OH megamaser at z>0.5. Marcin Glowacki et al. arXiv:2204.02523v1