Using the Hubble Space Telescope, astronomers have discovered a new type of cosmic object, a cloud of dark matter and gas that contains no stars. The object, located around 14 million light-years from Earth at the outskirts of the spiral galaxy Messier 94 (M94), has been nicknamed “Cloud 9.”
That’s a fitting nickname, given the delight scientists would have if Cloud 9 lives up to its scientific potential. The new object could not only potentially help explain how galaxies formed from gatherings of dark matter in the early universe, but could also grant insights into the very nature of this most mysterious “stuff.”
“This cloud is a window into the dark universe,” team member Andrew Fox of the Association of Universities for Research in Astronomy/Space Telescope Science Institute (AURA/STScI) for the European Space Agency (ESA), said in a statement. “We know from theory that most of the mass in the universe is expected to be dark matter, but it’s difficult to detect this dark material because it doesn’t emit light. Cloud-9 gives us a rare look at a dark-matter-dominated cloud.”
Dark matter is thought to account for around 85% of the “stuff” in the universe, but remains frustratingly invisible because it doesn’t interact with electromagnetic radiation such as light. That means scientists can only infer the presence of dark matter via its interaction with gravity and the influence that interaction has on ordinary matter and on light.
Outweighing the particles that comprise the atoms that compose stars, planets, moons, and everything we see around us on a day-to-day basis, dark matter is believed to have had a major influence in the early cosmos and in the shape of the universe as we see it today. This includes the matter that led to the first stars and galaxies coming together in regions of intense gravity where dark matter first gathered.
Such should also be the case with Cloud 9. Within this dark matter-dominated cloud, known as aReionization-Limited Hydrogen I Cloud (RELHIC), hydrogen gas has at least begun to gather — which would usually trigger stars being born from vast overdense patches in these clouds. However, star formation has failed to get started in the fossil remnant that is Cloud 9, likely because it seems to have failed to gather enough gas for star birth.
“This is a tale of a failed galaxy,” team leader Alejandro Benitez-Llambay of the Milano-Bicocca University in Milan, Italy, said in NASA’s statement. “In science, we usually learn more from the failures than from the successes. In this case, seeing no stars is what proves the theory right. It tells us that we have found in the local universe a primordial building block of a galaxy that hasn’t formed.”
Scientists have long theorized that RELHICs like this one exist, but they would have remained theoretical if it weren’t for Hubble.
“Before we used Hubble, you could argue that this is a faint dwarf galaxy that we could not see with ground-based telescopes. They just didn’t go deep enough in sensitivity to uncover stars,” team member Gagandeep Anand of STScI said. “But with Hubble’s Advanced Camera for Surveys, we’re able to nail down that there’s nothing there.”
The discovery of Cloud 9 indicates there may be many more relic-stalled galaxies out in the universe waiting to be uncovered.
“Among our galactic neighbors, there might be a few abandoned houses out there,” said team member Rachael Beaton, also from STScI.
RELHICs aren’t to be confused with hydrogen clouds around the Milky Way, which scientists have been studying for many years. Cloud-9 is smaller, more compact, and highly spherical, making it look very different from other hydrogen clouds. Its core is composed of neutral hydrogen and is around 4,900 light-years wide, with a mass estimated to be around 1 million times that of the sun. However, the mass of Cloud 9’s dark matter has been estimated at around 5 billion solar masses.
The team behind this discovery thinks that Cloud 9 has the potential to become a fully-formed galaxy full of stars at some point in the future, but only if it can gather up to 5 billion solar masses of hydrogen gas. For now, the fact that it lacks stars means that Cloud 9 offers scientists a unique opportunity to study dark matter clouds.
Meanwhile, astronomers will now be paying close attention to future astronomical surveys in the hope of discovering more failed galaxy RELHICs.
The team’s research was published in The Astrophysical Journal Letters and was presented at the 247th meeting of the American Astronomical Society in Phoenix on Monday (Jan. 5).