Enormous ghost galaxy orbiting the Milky Way

[ack]

Spectacular discovery

https://m.phys.org/news/2018-11-gaia-ghost-galaxy-door.html

Ant 2 is known as a dwarf galaxy. As structures emerged in the early Universe, dwarfs were the first galaxies to form, and so most of their stars are old, low-mass and metal-poor. But compared to the other known dwarf satellites of our Galaxy, Ant 2 is immense: it is as big as the Large Magellanic Cloud (LMC), and a third the size of the Milky Way itself.
What makes Ant 2 even more unusual is how little light it gives out. Compared to the LMC, another satellite of the Milky Way, Ant 2 is 10,000 times fainter. In other words, it is either far too large for its luminosity or far too dim for its size.
"This is a ghost of a galaxy," said Gabriel Torrealba, the paper's lead author. "Objects as diffuse as Ant 2 have simply not been seen before. Our discovery was only possible thanks to the quality of the Gaia data."

 

[astrotoy]

Very interesting. Probably the article means that it is very large spatially but not very dense (like Alaska in terms of square miles and people). However, it needs a minimum mass for its size to remain gravitationally bound for 10-13 billion years. I worked on the LMC while in college, measuring Cepheid variable stars in the Cloud. It will be very interesting to see what comes of this discovery. We have always assumed that what we see is what is out there. It may well be that there are a lot of Ant 2 like objects that make up a signficant fraction of the mass of the visible stuff in the universe, but are too faint for us to easily detect. Remember, this is one of the closest galaxies to us and we didn't know it was there. Much like having some house nearby that you had never seen before and had been there since the beginning of the neighborhood. How many houses like that are around?

If these are super, super common, they may be a partial solution to the dark matter problem.

Larry

 

[ack]

I bet this will throw off the merger simulations of the Milky Way and Andromeda too