Astronomers accidentally discover 'dark' primordial galaxy with no visible stars

Hydrogen gas in the primordial galaxy J0613+52 with red indicating regions turning away from Earth and blue showing regions turning toward us
Hydrogen gas in the primordial galaxy J0613+52 with red indicating regions turning away from Earth and blue showing regions turning toward us (Image credit: STScI POSS-II with additional illustration by NSF/GBO/P.Vosteen.)

Astronomers have accidentally discovered a dark galaxy filled with primordial gas untouched that appears to have no visible stars. 

The researchers behind the discovery say this galaxy, designated J0613+52, could be "the faintest galaxy found to date." Interestingly, scientists using the Green Bank Telescope (GBT) discovered the "dark" galaxy through a complete error. 

"The GBT was accidentally pointed to the wrong coordinates and found this object. It's a galaxy made only out of gas — it has no visible stars," Green Bank Observatory senior scientist Karen O'Neil said in a statement. "Stars could be there. We just can't see them."

Remarkably, this galaxy full of primordial gas isn't billions of light-years away and thus seen as it was when the 13.8 billion-year-old universe was in its infancy; instead, the dark galaxy designated J0613+52 is just around 270 million light-years away. 

Related: The mystery of vast 'cosmic ORCs' — odd radio circles that encompass entire galaxies — may be solved

Low Surface Brightness galaxies

J0613+52 was discovered by astronomers as they surveyed hydrogen gas in several so-called Low Surface Brightness (LSB) galaxies using several major radio telescopes around the globe, including the Green Bank Telescope (GBT), the world's largest fully steerable radio telescope located in Green Bank, West Virginia, and the Nançay Radio Telescope at the Paris Observatory.

LSBs tend to have a tiny population of stars spread across their volume, and as a result, they emit much less light per unit of area than standard galaxies like the Milky Way or Andromeda. LSBs are often barely brighter than the background luminosity of the night sky, making them incredibly tough to spot.

For instance, the first LSB to be discovered was Malin 1, found in the 1980s, which is still one of the largest spiral galaxies ever seen at 5 times the width of the Milky Way. Despite its size, though, Malin 1 is just 1% as bright as our galaxy.

LSBs also seem to be evolving much more slowly than other galaxies, with many still experiencing early stages of star formation. Astronomers believe this is because of their low gas density, meaning that overdense clumps of gas can't coalesce to that eventually birth stars.

The aim of the survey that found J0613+52 was to determine the mass and gas content of these low-brightness or "ultra-diffuse" galaxies, the diluted nature of which causes issues for current theories of star formation and galactic evolution. Astronomers noticed a disparity in data between the GBT and the Nançay Radio Telescope that would lead to the discovery of a galaxy that is an LSB unlike any other in the LSB survey.

A unique dark galaxy

J0613+52 is an LSB like the other 350 galaxies in the survey, but it has some properties that really set it apart.

"What we do know is that it's an incredibly gas-rich galaxy. It's not demonstrating star formation like we'd expect, probably because its gas is too diffuse," O'Neil said. "At the same time, it's too far from other galaxies for them to help trigger star formation through any encounters."

She added that this means that J0613+52 appears to be both "undisturbed and underdeveloped," hinting that what O'Neil and the team may have discovered accidentally in the shape of  J0613+52 is the first nearby galaxy made up of primordial gas.

This means gas made up of mostly hydrogen and helium created shortly after the Big Bang, which has not been enriched when stars exploded and seeded it with heavy elements, or "metals." This is something astronomers would normally see further away and thus much further back in cosmic history. 

Also remarkable about J0613+52 is the fact that it appears to be turning just like a normal spiral galaxy would 

Ultimately, the discovery of J0613+52 has left its discoverers with more questions than answers. Primary among these: Are there any more LSBs like this out there or is this a unique galaxy? 

The team suggests that deep imaging in multiple wavelengths of light could reveal more of these ultra-dark LSBs, though there is the possibility that the low density of gas makes these galaxies difficult or even impossible to observe at wavelengths other than radio waves. 

"A full sky survey by an extremely sensitive instrument like the Green Bank Telescope could uncover more of these objects," concluded O'Neil, who presented the team's findings at the 243rd meeting of the American Astronomical Society in New Orleans, Louisiana. 

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Robert Lea
Contributing Writer

Robert Lea is a science journalist in the U.K. whose articles have been published in Physics World, New Scientist, Astronomy Magazine, All About Space, Newsweek and ZME Science. He also writes about science communication for Elsevier and the European Journal of Physics. Rob holds a bachelor of science degree in physics and astronomy from the U.K.’s Open University. Follow him on Twitter @sciencef1rst.

  • Unclear Engineer
    I would like to know what the measured velocities of the gas show about the mass on this galaxy and the distribution of that mass in the radia parameter.
    Reply
  • RARRik
    DI'd the astronomers forget humans only see approximately 1% of the visible light spectrum no matter how the subject is enhanced to make it visible?
    Reply
  • George²
    Too transparent, the amount of matter is clearly negligible compared to a real galaxy. So, it is not, and certainly will never be, a galaxy at all.
    Reply
  • Torbjorn Larsson
    Nice find!

    Also remarkable about J0613+52 is the fact that it appears to be turning just like a normal spiral galaxy would.

    That seems to agree with new ideas on galaxy formation triggered by the observation of early spirals and even bars . The paper has notes on potential gas disks.

    “The dominant gas disc, by itself gravitationally unstable, potentially leads to the formation of a gas bar (Barnes & Tohline 2001), as an axisymmetric 100 per cent gas disc is theoretically proven to form a self-gravitating stable gaseous bar structure (Cazes & Tohline 2000).”

    The latter reference discuss gravitational convective and vorticity models and find the early spiral observed bending mode, with the convective “polytrope n=3/2” model recognizable as models for stars, star cores and gas planets . The “polytropic process” is a process of systems with energy transfers such as gas convection, so a stable dark and baryon matter gas only galaxy, and its rotation, seems eminently possible!
    Reply
  • Torbjorn Larsson
    RARRik said:
    DI'd the astronomers forget humans only see approximately 1% of the visible light spectrum no matter how the subject is enhanced to make it visible?
    Why would they forget!? And why is that relevant for looking for readily visible stars?

    George² said:
    Too transparent, the amount of matter is clearly negligible compared to a real galaxy. So, it is not, and certainly will never be, a galaxy at all.
    If astronomers define it as an LSB galaxy object instead of a gas cloud, why would anyone protest?

    Assuming the galaxy was part of the survey, the arxiv paper on the survey itself https://arxiv.org/abs/2307.11202] defines such a galaxy by its H I hydrogen line luminosity mass. It must be bright enough not to be confused with a regular but more diffuse gas cloud of the intergalactic medium:

    In principle, massive, or giant, LSB galaxies can be defined on different criteria. Based on surface photometry, Sprayberry et al. (1995) defined a “diffuseness index” to distinguish massive LSB galaxies, which is based on the deprojected blue central surface brightness µB(0) and the scale length of the disk hr – the 7 giants in their paper have⟨µB⟩ = 23.2 mag arcsec−2 and ⟨hr⟩ = 13.0 kpc. Other selection criteria can be used as well, such as: deprojected central blue disk surface brightness µB(0)≥ 23 mag arcsec−2 and H i mass MHI≥10^9.5−10 M⊙ or optical diameter≥50 kpc (e.g. Kulier et al. 2020; Mishra et al. 2017; Pickering et al. 1997). In the present study we use the criterion MHI≥10^10 M⊙ to identify massive galaxies, although we also consider the cases with high dynamical mass as defined by an inclination-corrected line width W50,cor ≥ 500 km s−1.
    Hence their criteria is not only expert but not subjective. Your personal criteria seem to fail on both these points to satisfy the demands of the expert community as they do galaxy science. It may be that the "massive" mass criteria failed this galaxy, but they discuss mass trends in the original LSB sample. "There are no obvious trends between the various measured global galaxy properties, particularly between mean surface brightness and galaxy mass."

    See also my own response to the article, where I relate science of gas cloud galaxies being predicted by models which also may have implications for early galaxy formation.
    Reply
  • George²
    I have some reservations about the quality of scholarly expertise lately. As is typical, they have been tromping around for more than a century with various hypotheses about general relativity and the other several dozen works of Albert Einstein and are constantly surprised by "discoveries" that they should have thought were ahead of them. And then, it's usually made clear that "their discoveries" were already reported by their predecessors in the good old 20th century, so these 2-3 new generations of scientists have discovered...nothing.
    Reply
  • tjowens
    RARRik said:
    DI'd the astronomers forget humans only see approximately 1% of the visible light spectrum no matter how the subject is enhanced to make it visible?
    Please look up the definition of visible, I don't think that word means what you think it means.
    Reply