Messier 94 is Lacking Galactic Neighbors

Messier 94 is Lacking Galactic Neighbors

Messier 94 is Lacking Galactic Neighbors
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According to a recent study conducted at the University of Michigan, Messier 94 has only 2 satellite galaxies.

Astronomers have long known that the Milky Way has around 10 smaller, satellite galaxies around it. Each of these galaxies has at least a million stars and this number can increase up to a billion in case of Magellanic Clouds. Powerful telescopes (Subaru telescope) allow the researchers to examine galaxies, which are 5 to 10 times the distance from the Milky Way. Once you could do that, you can use the Physics of how galaxies form around the Milky Way to predict the number of satellite galaxies around a distant, Milky Way-sized galaxy.

Messier 94 is Different

The researching team studied one such galaxy, called Messier 94 (M94). They expected to get a similar quantity of satellite galaxies but found only 2 galaxies with very few stars in each one of them. This finding is quite surprising for scientists as it has created several new questions about the current understanding of how galaxies form, which is indirectly linked with Dark Matter. Adam Smercina, a National Science Foundation Fellow at the Department of Astronomy in the University of Michigan who led this research, talked about that and said,

More than just an observational oddity, we show that the current crop of galaxy formation models cannot produce such a satellite system. Our results indicate that Milky Way-like galaxies most likely host a much wider diversity of satellite populations than is predicted by any current model.

Galaxy Formation

The gravitational force of the halos of dark matter (around galaxies) is extremely strong. Consequently, they can attract a substantial amount of surrounding gas from their immediate vicinity. Massive galaxies like ours are generally formed in halos of the same size but these satellite galaxies are produced in smaller sub-halos which puts a big question mark on their dependability.

If the production rate of high-mass stars (in these satellite galaxies) increases too much, their eventual supernova explosions will stop the growth of the galaxy by expelling all the gas. Having said that, scientists are still unsure about the size of halo for which this scattering in galaxy formation becomes important. Messier 94 showed that the uncertainty of galaxy formation is much more in intermediate-sized dark halos. Smercina acknowledged that in the following words:

“We think that that scatter — the range of galaxies we expect to see — maybe a lot higher than what people currently think for dark matter halos of a certain mass. Nobody’s under any illusions as to there being this huge scatter at the very lowest halo masses, but it’s at these intermediate dark matter halos that the discussion is happening.”

Composite Image of Messier 94

The researchers took a composite image of M94 in order to observe the number of satellite galaxies around this humungous galaxy. The image captured around 12 square degrees of the night sky. For comparison, the full moon takes about one square degree. Although such an image covers a lot of sky around the target (Messier 94), it is accompanied by layers and layers of noise (scattered light and cosmic rays), which makes it incredibly hard to detect faint dwarf galaxies.

For sake of avoiding any error (missing any satellite galaxy), the researching team artificially engineered the missing galaxies into the image and recovered them using the same methods as for real galaxies. Once they were confident that there are no other satellite galaxies around Messier 94, the researchers announced that there are only two galaxies around M94. Smercina referred to the curiosity of this discovery by saying,

“The real kicker is whether or not the community expected this could be possible. That is the real curiosity of this finding — the result is something the simulations don’t predict. When you can discover something we didn’t really think we could find, you can make a contribution to our understanding of how our universe works, that’s really rewarding.”   

You can get a glimpse of this lonely galaxy in the following video:

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