South Africa’s radio telescope the MeerKAT, which is the precursor of the giant Square Kilometre Array (SKA) telescope, continues to make new discoveries.
An international team led by astronomers – professors Gyula Józsa, Michelle Cluver and Thomas Jarrett − utilised the South African MeerKAT radio telescope to discover a mysterious chain of hydrogen gas clouds the size of a massive galaxy.
In a statement, the South African Radio Astronomy Organisation (SARAO) says the accumulation of so much elemental hydrogen without associated stellar components is the largest yet discovered.
It says appearing at the edge of a relatively massive group of galaxies, there is the possibility that the cloud chain is gas stripped from group-member galaxies, but it may also be primordial and gravitationally drawn into the group through a cosmic filament pathway.
Whatever the case, SARAO says MeerKAT is proving to be a ground-breaking telescope, and this “dark” cloud discovery should soon be followed by many such discoveries in the exciting days ahead.
The discovery of the mystery clouds will be published in the renowned Astrophysical Journal under the title: “The detection of a massive chain of dark HI clouds in the GAMA G23 Field”.
A precursor to the SKA, South Africa’s MeerKAT telescope located in the Northern Cape was launched in 2018. It aims to answer fundamental astrophysical questions about the nature of objects in the Universe.
The MeerKAT is currently made up of 64 dishes, each 13.5m in diameter.
Totally unexpected
Of late, the MeeKAT has made several ground-breaking discoveries. Last month, the radio telescope revealed new, previously unseen cosmic puzzles.
In June, the telescope produced a striking image showing a combination of cosmic features never before seen, revealing unexpected details of the inner workings of enormous radio galaxies.
Last year in April, an international team of astronomers uncovered unusual features in the radio galaxy ESO 137-006 using MeerKAT data.
Explaining the new discovery, Cluver from Swinburne University explains: “Cosmic filaments are the highways along which mass concentrations come together under the action of gravity.
“We expect gas-rich galaxies to be associated with these structures, using their neutral hydrogen as fuel for star formation and growth. We, therefore, designed our blind shallow survey to search for this type of gas along such a filament. And, indeed, we found gas in many galaxies, but we did not expect anything like these clouds. They form a huge complex of tenuous atomic hydrogen gas that stretches over a distance of 1.3 million light years. Seven spots of concentrated gas can be discerned from the complex,” says Cluver.
SARAO notes the puzzling thing is that despite its extraordinarily large gas mass (equivalent to 10 billion of our Sun’s mass), there are close to no stars in the vicinity of the complex.
It explains that normally, any cool gas like atomic hydrogen is associated with their “home” galaxy, where the gas reservoir continues to feed and grow the galaxy over eons of time.
Such a large cloud simply cannot survive on its own – floating freely, the local environment is far too harsh as it gets heated up and ionised by the radiation from surrounding galaxies, says the organisation. It adds that only the gravitational pull of a galaxy can, in principle, compact a cloud to a degree where it gets dense enough to create a natural shield against the cosmic background radiation.
Space mystery
Jarrett from the University of Cape Town says: “We were very surprised that we did not find any indication of a significant amount of stars, despite our thorough search using very deep ultraviolet, optical and infrared imaging. There have to be stars; it’s inconceivable for a cloud the size of a galaxy to simply be floating in space.”
SARAO believes there is one possible exception to this, where a small dwarf galaxy is seen close to one corner quadrant of the cloud complex, leaving at least six dark clouds.
Yet it is far too small to possibly be the origin of all this gas, it notes.
Józsa from the Max-Planck-Institute for Radio Astronomy and Rhodes University explains: “Only a handful of cloud complexes with similarities to this one are known and our new discovery seems to differ in some key aspects.
“The simplest explanation would be that of a tidal interaction between galaxies, the gas being ripped out of the host galaxies in a close encounter. But how the six of seven supermassive concentrations without any stars can be formed in such an event still needs to be explained,” says Józsa.
SARAO points out that no obvious connection to any donor galaxy is evident from the data. It says the existence of these “dark clouds” is hence a mystery yet to be solved.
“Maybe the complex enters the group for the first time, consisting of primordial gas gravitationally pulled into the galaxy group along a cosmic filament. Now that the clouds have been discovered, the researchers hope that it will be possible to learn about their origin using dedicated, much deeper, observations with several telescopes in the southern hemisphere,” the organisation says.
“Solving this puzzle could have interesting implications for our understanding of the role that atomic hydrogen plays in how galaxies evolve in large-scale structures.”
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