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Hubble and the VLT Uncover Evidence For Self-Interacting Dark Matter
astroengine writes: A new study carried out by the ESO's Very Large Telescope and the NASA/ESA Hubble Space Telescope has revealed for the first time that dark matter may well interact with itself — a discovery that, at first glance, seems to contradict what we thought we knew about the nature of this invisible mass. "In this study, the researchers observed the four colliding galaxies and found that one dark matter clump appeared to be lagging behind the galaxy it surrounds. The dark matter is currently 5000 light-years (50 000 million million kilometers) behind the galaxy — it would take NASA’s Voyager spacecraft 90 million years to travel that far. A lag between dark matter and its associated galaxy is predicted during collisions if dark matter interacts with itself, even very slightly, through forces other than gravity. Dark matter has never before been observed interacting in any way other than through the force of gravity."
In a rush to tailor the evidence to a flawed theory, dark mentor was invented by humon minds in an attempt to save a beloved theory. We need to cast off the shackles of what we want to be true, and look at the evidence in a cold, anyalytical light. When this is done, I'm quite certain that there will be no need for the magical fairy dust matter that is there but isn't there.
No, because there would be no easy way for the particles to shed momentum and form a clump.
Even when you have a black hole pulling on normal matter, stuff can't easily just fall in. If you had a black hole and a single piece of something falling toward it, unless that piece directly hits the event horizon or comes close to it, it will just fling back out at the really close to the same speed it went in (if it was massive enough and in a small orbit, the orbit might decay from gravity waves, but that is still a slow process and not applicable to smaller dark matter candidate particles). When you have a bunch of stuff forming an accretion disk, the process of exchanging momentum so that some matter falls further in is a complicated process, often coming down to plasma physics effects like the magneto-rotation instability.
So you end up with a large cloud of dark matter, because the particles pass through each other and just all orbit a center of mass. Very slowly, particles can exchange momentum with other dark matter particles, flinging some out of the system as a way of shedding energy and momentum. But the timescale it would take for that to allow them to cool off significantly is longer than the current age of the universe.
The dark matter is currently 5000 light-years (50 000 million million kilometers) behind the galaxy —
it would take NASA’s Voyager spacecraft 90 million years to travel that far.
Right. Would it? Okay. How is that supposed to help me imagine 5000 light years? I already know it's a bloody long way. You might as well have told me it was the length of x football pitches or y times the length of the Amazon river.
A comparison with the diameter of the galaxy in question would have been more useful.
systemd is Roko's Basilisk.