NASA’s Hubble Telescope A Galaxy That Is 99% Dark Matter

Hubble Telescope Discovers Rare Galaxy That Is 99% Dark Matter

Astronomers using the Hubble Space Telescope have identified one of the most extreme galaxies ever observed, a faint, ghostly system composed of an astonishing 99% dark matter. “All galaxies are dominated by dark matter, an invisible “stuff” that outweighs all of the matter comprising stars, planets, and moons by around five to one. But in some galaxies, dark matter takes this domination to the extreme,” according to Space.com.

Unlike familiar spiral galaxies such as Milky Way, which shine brightly with hundreds of billions of stars, this newly studied system contains relatively few stars. Measurements of its gravitational influence reveal that it is far more massive than its dim appearance suggests, which essentially indicates that almost all of the mass is made up of pure dark matter.

The Cosmos

Dark matter is one of the greatest unsolved mysteries in astrophysics. Though invisible, it exerts gravitational force and is believed to account for roughly 85% of all matter in the universe. Galaxies are thought to form within vast halos of dark matter, which act as gravitational anchors, pulling in gas that later forms stars. In most galaxies, dark matter outweighs normal, or “baryonic,” matter by a factor of about five to one.

But in this case, the ratio is dramatically higher. Researchers estimate that visible matter, stars and gas, makes up only about 1% of the galaxy’s total mass. The rest is dark matter, making it one of the most dark matter-dominated galaxies ever identified.

The team used high-resolution imaging from Hubble to measure the motions of globular clusters, dense groups of stars that orbit the galaxy. By tracking how quickly these clusters move, astronomers can infer the galaxy’s total gravitational pull. The faster the clusters move, the more mass must be present to hold them in orbit. The results showed a surprisingly strong gravitational field relative to the galaxy’s faint luminosity.

An Oddity

Ultra-diffuse galaxies are not entirely new to astronomers. Over the past decade, dozens have been discovered in galaxy clusters, appearing as faint, extended patches of light. They are roughly the size of the Milky Way but contain only a tiny fraction of its stars. Some UDGs have sparked controversy because they appeared to contain little or no dark matter, challenging conventional galaxy formation models.

This newly analyzed galaxy represents the opposite extreme. Instead of lacking dark matter, it seems almost entirely composed of it. “The authors pooled data from the Hubble, Euclid, and Subaru telescopes, three of the most powerful observatories available. This residual light is a clear sign of an underlying galaxy so dim that the three telescopes missed it on their own,” according to Wired.

“This is about as dark as a galaxy can get,” one researcher involved in the study said. “It pushes the limits of what we thought possible.”

This find is simply showing that galaxies can form in many more ways that is much wider than anyone previously thought before.

Formation of Galaxies

How does a galaxy end up with so little visible matter? Scientists have proposed several possibilities.

One theory suggests that intense bursts of star formation early in the galaxy’s history may have blown much of its gas away.

Another possibility is that the galaxy formed in isolation, in a region where gas density was too low to produce many stars. Without sufficient raw material, star formation would have been stunted from the beginning.

Illumination

Finding galaxies that are overwhelmingly dominated by dark matter offers a unique laboratory for testing theories about the substance’s nature.

If dark matter behaves differently than current models predict, subtle discrepancies might show up in systems like this one. For instance, the distribution of dark matter within the galaxy, whether concentrated at the center or spread more evenly, could reveal clues about its fundamental properties.

The composition of the entire galaxy may help astronomers refine simulation of cosmic evolution. There are many computer models that are attempting to replicate how galaxies are formed, that way astronomers and scientists are able to understand more or less how this process happens.

A Continuing Legacy

Launched in 1990, the Hubble Space Telescope has transformed humanity’s view of the cosmos, from measuring the universe’s expansion rate to capturing breathtaking images of distant nebulae. More than three decades into its mission, Hubble continues to deliver discoveries that reshape astrophysics.

Looking Ahead

If more 99% dark matter galaxies are found, they could reshape our understanding of galaxy formation and the cosmic web. Even if this object proves rare, it stands as a striking example of the universe’s capacity for surprise.

Sources:

Space.com: Hubble telescope discovers rare galaxy that is 99% dark matter

Wired: A Galaxy Composed Almost Entirely of Dark Matter Has Been Confirmed

Featured Image Courtesy of Steven Miller’s Flickr Page – Creative Commons License

Inset Image Courtesy of kristian fagerstrom’s Flickr Page – Creative Commons License