Re: This Week's Finds in Mathematical Physics (Week 238)

[John Baez]

Some updates on the Bullet Cluster / dark matter saga.
You can now see a picture of the Bullet Cluster here:

http://math.ucr.edu/home/baez/week238.html

I've also updated a bunch of information and fixed some mistakes
in the initial version of "week238", thanks in part to Matt Owers.

>Markevitch and company have been studying the "Bullet Cluster", a
>a bunch of galaxies that has a small bullet-shaped subcluster zipping
>away from the center at 4,500 kilometers per second.

>It seems that one of the rapidly moving galaxies in this subcluster
>has hit a bystander galaxy - I'm not sure, but a high-speed collision
>of galaxies occurred.

In fact, the whole subcluster hit another subcluster!

So, the picture is a picture of colliding bunches of galaxies.
The individual galaxies in these bunches mainly shoot right past
each other - but the intergalactic gas in one bunch is hitting
the gas in the other, and getting so hot it emits X-rays.

>So, dark matter is seeming more and more real. In fact, last year
>folks found evidence for "ghost galaxies" made mainly of dark matter
>and cold hydrogen, with very few stars:
>
>6) PPARC, New evidence for a dark matter galaxy,
>http://www.interactions.org/cms/?pid=1023641

Apparently the consensus is now that this ghost, VIRGOHI 21,
is hydrogen stripped off from a galaxy by the "wind" it felt
as it fell into the Virgo Cluster. This effect is called
"ram pressure stripping" - the gas of a galaxy can be stripped
off if the galaxy is moving rapidly through a cluster, due
to interaction with the gas in the cluster.

 

[Kwok Man Hui]

On Thu, 17 Aug 2006, John Baez wrote:
>
>> Markevitch and company have been studying the "Bullet Cluster", a
>> a bunch of galaxies that has a small bullet-shaped subcluster zipping
>> away from the center at 4,500 kilometers per second.
>
>> It seems that one of the rapidly moving galaxies in this subcluster
>> has hit a bystander galaxy - I'm not sure, but a high-speed collision
>> of galaxies occurred.
>
> In fact, the whole subcluster hit another subcluster!
>
> So, the picture is a picture of colliding bunches of galaxies.
> The individual galaxies in these bunches mainly shoot right past
> each other - but the intergalactic gas in one bunch is hitting
> the gas in the other, and getting so hot it emits X-rays.
>
>> So, dark matter is seeming more and more real. In fact, last year
>> folks found evidence for "ghost galaxies" made mainly of dark matter
>> and cold hydrogen, with very few stars:
>>
>> 6) PPARC, New evidence for a dark matter galaxy,
>> http://www.interactions.org/cms/?pid=1023641
>
> Apparently the consensus is now that this ghost, VIRGOHI 21,
> is hydrogen stripped off from a galaxy by the "wind" it felt
> as it fell into the Virgo Cluster. This effect is called
> "ram pressure stripping" - the gas of a galaxy can be stripped
> off if the galaxy is moving rapidly through a cluster, due
> to interaction with the gas in the cluster.
>
>Along with your above comment on "ram pressure stripping",
I would like to talk about an old This Week's Finds, Week 224, about a
mono knotted jet from a hypothesized supermassive black hole in M87 galaxy.

The three pictures from NASA do not show two knotty jets. There is only
one jet revealed. I have reviewed several times that the Chandra X-ray
telescope picture has shown that there is dim blue light around the
brightest center spot. So there are matters or gases around the
hypothesized supermassive black hole. Therefore, there should have another
jet (synchrotron radiation) from the acretion disk of the black hole and
that jet should x-ray the inter-galaxtic matters/gases on the other side
of the acretion disk as well. However, none is seen.

Would it be possible that there was a high speed small dense dark matter
(High speed ,dense and small are required so that it didn't cause a
prolonged microlensing effect that can be observable nowaday.)
"ram pressure stripping" some tiny galaxies and brought those gases to the
current scene? And the small dense dark matter finally hit the center
of the M87 galaxy and formed a black hole (if there is a black hole)?
Look at the Chandra x-ray picture, and notice the blurryness and a very
bright spot near the jet tail. Do they look like the remaining part of the
"bullet cluster"?

 

[tacman]

Thank you for the update on the Bullet Cluster and the ongoing research on dark matter. It's fascinating to see how new evidence and discoveries are shedding light on the mysterious nature of dark matter. The picture of the colliding galaxies is truly remarkable and helps to visualize the intense interactions happening in the cluster.

The finding of "ghost galaxies" made mainly of dark matter and cold hydrogen is also intriguing. It's exciting to see how our understanding of dark matter is evolving and how it plays a crucial role in the formation and evolution of galaxies.

The concept of "ram pressure stripping" is also interesting and provides a possible explanation for the appearance of ghost galaxies. It's amazing to see how the interplay between different forces in the universe can result in such complex and dynamic phenomena.

Overall, the updates on the Bullet Cluster and dark matter are a testament to the ongoing advancements in mathematical physics and the tireless efforts of researchers in this field. Thank you for sharing this information and providing a deeper understanding of these fascinating topics.