Astronomers using Hubble Space Telescope Just discovered a new type of celestial object: Cloud 9, starless, gas-rich dark matter cloud it was too easy to become a full-fledged galaxy.
As detailed in a study published Nov. 10 in Letters from an Astrophysical Journal This strange object, presented this week at the 247th meeting of the American Astronomical Society in Phoenix, is located more than 14 million light-years from Earth, near the spiral galaxy Messier 94 (M94). Cloud 9 is a cosmic relic, the primordial building block of galaxies, which confirms the threshold of critical mass required for the collapse of a body of gas and dark matter into a galaxy.
As a result, the discovery of Cloud 9 strongly supports the cornerstone of a leading cosmological concept that aims to explain the structure and composition of the Universe—the lambda cold dark matter model (LCDM). One of the main predictions of the model is that dark matter settles into haloswhich may or may not become heavy enough to anchor galaxies.
“There should be many such ‘dark halos’, but most of them do not retain hydrogen gas, so they remain invisible,” Deep Anandan astronomer at the Space Telescope Science Institute (STScI) and lead author of the study, told Live Science via email. “Cloud 9 is at the very upper end of the dark halo mass range, which allows it to retain gas and therefore be visible through radio observations. This is truly compelling confirmation of LCDM's cornerstone prediction.”
Accordingly, Cloud 9 offers the first hint of evidence that the Universe may be replete with low-mass dark matter halos that, as theory predicts, remain devoid of stars.
Digging up a space fossil
Astronomers discovered Cloud 9 three years ago using Five hundred meter aperture spherical telescope (FAST) to Guizhou, China. The massive radio telescope has been “very productive in finding similar clouds” and may find others in the future, study co-author Andrew Foxalso an astronomer at STScI, told Live Science via email.
Previously, researchers used the Very Large Array, a group of 28 telescopes in New Mexico, to focus on the peak of Cloud 9's radio emission emanating from its 5,000 light-year-wide core. However, observations were unable to determine the true nature of the object, possibly due to limitations in the telescope's sensitivity. Perhaps Cloud 9 was simply a dwarf galaxy that was too dim to be properly seen by ground-based objects, the researchers suggested.
But as described in a new study, follow-up observations with the Hubble Space Telescope's Advanced Survey Camera revealed a much rarer phenomenon that astronomers have been searching for for years: a “theoretical phantom object” and the first-ever confirmed RELHIC, or reionization-limited HI cloud. In other words, it is a cloud of neutral hydrogen, an ancestral remnant of early space and a unique “window into the dark universe,” Fox said in an interview. NASA Press Statement.
This discovery of hydrogen was proof that Cloud 9 is not a typical dwarf galaxy, but something stranger.
To be or not to be a galaxy
Researchers analyzed the gas in Cloud 9 based on the radio waves it emitted and found that the gas accounts for the strange object's mass equal to about one million suns. This alone is not enough to contain such a large gas cloud. So, if we assume that the system is maintained due to the balance between gravitygas pressure and gas heating, the dark matter component of Cloud 9 should weigh about five billion solar masses, the team calculated.
This mass falls into the sweet spot, “surprisingly close” to the independently theoretically based critical mass threshold. At this threshold, Cloud 9 lacks enough mass to become a galaxy, but is massive enough due to its dark matter component to hold itself together.
Cloud 9 is also in thermal equilibrium with cosmic ultraviolet (UV) backgroundultraviolet energy coming from all the stars in the universe, active black holes and hot gas. This energy keeps the gas ionized, or electrically charged, and relatively hot, suppressing the formation of galaxies. This also contributes to the complete absence of stars in the cloud.
However, researchers conclude that Cloud 9 may not be irrevocably doomed to eternal darkness. It could still gain enough mass to become a galaxy, although the exact mechanics that would allow this to happen are speculative.
Whatever the fate, Cloud 9 serves as a physical benchmark that shows that current models of dark matter, as well as galaxy formation theories are on the right track.
An extremely rare relic from the ancient universe.
Future research will look for failed galaxies like Cloud 9, although finding them is much easier said than done for several reasons. First, such dim objects are easily eclipsed by other celestial sources.
These clouds are also ephemeral and will likely be destroyed by a process known as stripping under plunger pressurewhich deprives them of gas as they move through intergalactic space. In fact, according to the researchers, Cloud 9 appears to already be perturbed by the relatively hot circumgalactic environment around the neighboring galaxy M94.
“To survive as a dark, gas-rich cloud today, a system must meet two stringent and statistically rare criteria,” Alejandro Benitez-Llambayprincipal investigator of the Cloud 9 program and astrophysicist at the University of Milan-Bicocca, Live Science told Live Science via email. “First, its dark matter halo should have an atypically slow assembly history; if it had grown too quickly in the early Universe, the gas would have collapsed to form stars before the cosmic UV background could heat it. Secondly, the system must remain sufficiently isolated.” Less than 10% of such gas clouds may have remained as starless and untouched as Cloud 9, Benitez-Llambay added.
Finally, as an ambassador of the dark universe, Cloud 9 is a crucial reminder that the stunning panoramas of stars we see in most astronomical images represent small share about the cosmos as a whole—the shiny things we see tell only part of the cosmological story.
