The Enigma of Dragonfly 44, the Galaxy That’s Almost Invisible

The discovery of a dim, broad and heavy galaxy must be almost completely invisible, according to a bombshell paper published in 2016 by an astronomer. The galaxy is 99.99 percent dark.

There was a heated debate about the properties. More than a thousand similar but faint galaxies have turned up.

Ultra-diffuse galaxies are also known as Dragonfly 44. Paul Bennet, an astronomer at the Space Telescope Science, said that UDGs are so dim that it is difficult to see them in a telescope survey. There is no bright star-forming gas in UDGs, leaving only a skeleton of elderly stars.

The existence of them has caused a stir in the theory. They didn't show up in simulations. You have to do something special to make a large and faint universe.

There are new theories explaining how UDGs came about. The smudges of light may be new evidence of dark matter.

There is too much dark matter.

As gravity brings clumps of gas and stars together, their combined energy and momentums cause the mashup to spin. A new universe emerges.

There is a single problem. They should come apart as the universe rotates. They don't seem to have enough mass to hold together. Dark matter provides missing gravity. There is a large conglomeration of nonluminous particles. The dark matter is holding the galaxy together.

Counting its spherical clusters of stars can be used to estimate a galaxy's rotation speed. "We don't know why, from a theory point of view, but the number of these 'globular clusters' correlate closely with those harder-to-measure properties." The number of clusters counted in the 2016 paper implied a large dark matter halo.

No one had seen something like that before. According to Van Dokkum and co-authors, a large dark matter halo that robbed it of its star-forming gas could be the reason for the failure of the Milky Way.

There is no dark matter.

Dark matter doesn't exist at all, according to another camp of astronomy. The researchers explain missing gravity by tweakingNewton's law of gravity.

The mass-to-light ratio of the stars is used to calculate the modified gravity for each galaxy. MOND theorists don't speculate as to why the force would depend on this ratio, but their formula matches the observed speeds of most galaxies.

The astronomer at Case Western Reserve University calculated from the mass-to-light ratio that it should be more slowly rotating than van Dokkum estimated. The calculation didn't fit the data