
Mystery in the Perseus Cluster - uladzislau
http://science.nasa.gov/science-news/science-at-nasa/2014/24jul_perseuscluster/
======
xioxox
I've worked quite a bit on this object. The Perseus cluster is one of the most
interesting galaxy clusters in the sky and is the X-ray brightest (and so well
studied). There's star formation, bubbles of relativistic plasma bubbles
generated by the central black hole, presumably heating the surrounding gas
and preventing catastrophic cooling, sound waves generated by the inflation of
the bubbles, a giant nebula producing emission lines. You could give several
talks about this object... Some nice pics here of the central galaxy, NGC1275:
[http://www-xray.ast.cam.ac.uk/papers/ngc1275/](http://www-
xray.ast.cam.ac.uk/papers/ngc1275/)

We'll have to wait to see if this result can be replicated by others and we'll
look at the results from ASTRO-H when it launches. If you examine at the
original paper
([http://arxiv.org/abs/1402.2301](http://arxiv.org/abs/1402.2301)), it's
certainly not cut and dried dark matter emission (yet).

~~~
jgraham
(/me waves at xioxox)

It may be worth noting the significance of ASTRO-H to this kind of science
(full disclaimer: it's a long time since I did any astrophysics so I am liable
to get things wrong). The attraction of ASTRO-H is not just newer == better.
In fact in several ways it's worse than existing X-ray satellites, for example
it won't have the angular resolution of Chandra (so no pretty pictures) or the
sensitivity of XMM-Newton (so bad for looking at very faint objects). Where it
is designed to excel, however, is in spectral resolution, where it is about an
order of magnitude better than the other observatories. This means it's going
to be great at measuring the precise energy of incoming X-rays, which is
essential for studying emission lines like this. If your spectral resolution
is too low you'll find it difficult to detect weak lines at all because they
get averaged over such a big energy range that they end up just looking like
the background emission from the hot plasma in the cluster.

Once you have established that there is a line in the emission, good spectral
resolution is also critical to determining which models are compatible with
it. There's almost certainly a lot of ideas people can dream up that will fit
"a vauge bump around 3.55keV", many of which will be eliminated once you have
a better idea of the shape of the line. This is the sort of science that
ASTRO-H should be good at.

Hopefully someone will correct me if I made any egregious errors.

~~~
xioxox
(/me waves back at jgraham)

Absolutely right - ASTRO-H brings new capabilities - high spectral resolution
in X-rays which we don't have now. It's pretty exciting.

Beyond that, here in Europe, the European Space Agency has now approved our
proposal for Athena
([http://www.mpe.mpg.de/Athena](http://www.mpe.mpg.de/Athena)), which should
provide a large collecting area, high spectral resolution and pretty good
spatial resolution. It's going to be a large technical challenge, which
unfortunately means we'll have to wait until 2028 for launch. It requires
development of a new mirror technology (based on stacks of silicon chip
wafers!), development of a cryogenic X-IFU (X-ray integral field unit), which
is going to provide spatially-resolve high spectral resolution X-ray
spectroscopy. There's also a wide field imager, capable of mapping large areas
of the sky quickly.

------
vesinisa
This is exactly what drives real science. First we gather data and make sure
that data is valid, then we compare it to our predictions (model), and if not
all things are explained by the model, we start refining the model. In the
process, our understanding of the world becomes ever more comprehensive. So in
short, data not agreeing with the model is the best possible scenario.

~~~
asuffield
Yup. This is awesome. It's been a while and an awful lot of work since
somebody found evidence of some new physics. The LHC has been a bit of a
disappointment so far - it has yet to surprise us.

~~~
signa11
higgs boson ?

~~~
jerf
[http://www.theatlantic.com/technology/archive/2012/07/why-
th...](http://www.theatlantic.com/technology/archive/2012/07/why-the-higgs-
boson-discovery-is-disappointing-according-to-the-smartest-man-in-the-
world/259468/) \- and while that probably isn't the best link it links to
several other useful things as well. Unfortunately, we pretty much found the
Higgs in the general range we expected it to be, which was in some ways the
worst possible outcome, and certainly the least surprising.

------
DanielBMarkham
Anybody care to give a layman/HS explanation of why this might be dark matter?

It's been a long time since High School chemistry class, but as I remember it,
spectral emission lines are caused by electrons changing orbital levels and
thereby releasing a photon. So dark matter has electrons? Er, would that mean
that it's not dark? Why wouldn't this just mean that we've missed an orbital
level somewhere?

~~~
ajross
Yes, if it interacts with photons it means that it's not "dark". But the
problem is that atomic physics is awfully well travelled, the chances that
we've "missed an orbital" somewhere in a conventional material seems slim (or
at least it does to the authors -- I'm not an expert).

So a novel photon interaction in intergalactic space would be huge news even
if it doesn't map directly to dark matter.

~~~
privong
There is lots of unexplored territory in molecular spectroscopy. The ALMA
Telescope[0]—primarily operating at millimeter and sub-millimeter wavelengths,
where the bulk of molecular transitions are—is likely to discover many
spectral lines which have not been classified. Estimates suggest that 50–80%
of the lines seen in some observations will correspond to unknown transitions
of known molecules or transitions from previously unknown molecules. But the
energies of molecular (rotational) transitions are generally far too low for
an unknown molecular species to be a viable explanation for a spectral line in
the X-rays.

[0]
[https://en.wikipedia.org/wiki/Atacama_Large_Millimeter_Array](https://en.wikipedia.org/wiki/Atacama_Large_Millimeter_Array)

------
jdubya
The Perseus Cluster is probably one of the most interesting galaxy clusters I
have every had the privilege of studying.

Anyone interested in the universe should take a quick gander at this massive,
massive scientific wonder.

New physics!

------
pavel_lishin
Wait, so there are thousands of galaxies, all of them inside a cloud of
relatively dense, incredibly hot gas? And it also contains a very energetic
source of energy in the middle?

I'm imagining a boiling ocean, covered in volcanoes, with a nuclear bomb going
off in the middle of it.

~~~
Sharlin
Well, "relatively dense and incredibly hot gas" in this context means "still
indistinguishable from vacuum without sensitive sensors, even if you were
immersed in it".

~~~
pavel_lishin
Hm, I thought it said it was in the multi-million degree temperature range. I
guess you can still have near-vacuum atoms at a pretty high temperature.

------
chiph
What, no Omicron Persei 8 or Lrrr jokes?

------
bellerocky
This seems like a better source:

[http://science.nasa.gov/science-news/science-at-
nasa/2014/24...](http://science.nasa.gov/science-news/science-at-
nasa/2014/24jul_perseuscluster/)

~~~
WaxProlix
Thanks, the writing alone on that other one was atrocious.

~~~
houseofshards
Precisely ! Fe XXV ? That sounds a bit like descendent from a long line of
monarchs.

~~~
guard-of-terra
NASA site spells it the same. Presumably it's how physicists call ions.

~~~
tinco
I learned to spell ions like that in highschool, though never more than Fe
III, I think.

------
duggan
If one of the engineers responsible for developing the technology had written
this headline: "Possible Widespread Bug In X-ray Telescopes Uncovered"

~~~
InclinedPlane
That was indeed the original assumption when the Cosmic Microwave Background
was detected. The problem with the CMB, from an observational standpoint, is
that it's enormously uniform. It differs by only a few parts per million
across the sky. Which means that when you perform observations with less
sensitive equipment the signal tends to look like a uniform noise source. But
it really does come from the sky, as we eventually figured out.

~~~
srean
I think Nobel committee did Ralph Alpher deep disservice. He had not only
conjectured the existence of CMB radiation but also computed properties the
radiation would have. The Nobel instead went to two radio engineers who
happened to chance upon CMB purely by accident.

George Gamow, his advisor, thought it would be funny to include Hans Bethe as
a coauthor for Alpher's original research, just for the author list "Alpher,
Bethe, Gamow". Bethe was not involved in anyway in that piece of research.

More here
[http://en.wikipedia.org/wiki/Ralph_Asher_Alpher#Big_Bang_nuc...](http://en.wikipedia.org/wiki/Ralph_Asher_Alpher#Big_Bang_nucleosynthesis_theory)

If you have not read Gamow's popular science writings.... highly recommended.

~~~
hvs
Experimentalists often tend to get more credit than theoreticians. People
(apparently along with the Nobel committee) prefer results over potential
theories.

~~~
mannykannot
That appears to be so, but the committee's application of that preference is
rather self-contradictory. Without an explanation, the result would not even
have been a contender for the prize, and it was Alpher who first provided the
explanation.

As Alpher also showed that the universal ratio of hydrogen and helium isotopes
can be explained by nucleosynthesis in the big bang, he seems to have been
seriously overlooked.

~~~
hvs
Just to be clear, I'm not endorsing the committee's views, just stating them.
I agree that Alpher deserves more attention and credit for his work.

------
pistle
Buzzfeed style headlines. Article includes this gem:

'The menagerie of dark matter candidates that might produce this kind of line
include axions, sterile neutrinos, and "moduli dark matter" that may result
from the curling up of extra dimensions in string theory.'

1) Assumption of dark matter 2) String theory

It's never hard to find a group of theoretical physicists willing to tag
anything currently, poorly misunderstood as most likely an effect of dark
matter and string theory.

And, of course, this will require a new observatory.

~~~
DCKing
The headline perfectly summarizes that this observation is unexaplained by
modern physics. You are right that associating this with dark matter and
string theory is unfounded speculation, but there's nothing wrong with the
headline.

Also, a new observatory is a good thing. Bring it on.

~~~
pistle
Which is why they changed the headline. "Bring em on." \- George W. Bush

------
Tycho
This observation notwithstanding, if dark matter cannot be observed, isolated
or detected, then why should we treat it as anything more than an arbitrary
hypothesis? Why not dismiss it similar to how we dismiss the idea that God
created the universe, or indeed that God is holding the cosmos together?

~~~
kryptiskt
The reason that we are talking about dark matter is that it is detectable by
its gravitational effects on ordinary matter. Our ways of looking at it are
still incredibly blunt but they're much better than what we had 20 years ago.
We can make hypotheses about dark matter and conceive observations to test
these hypotheses.

As for dismissing God, I don't see why, we just need to come up with some
signature that would differ between a designed universe and an accidental one
and apply for observation time on a suitable instrument.

~~~
javert
Dark matter has a different cognitive status than God, because there is some
evidence, albeit inconclusive, that suggests dark matter (from what I
understand; IANAP). In contrast, there is no evidence that suggests God, so a
claim that God exists would be arbitrary and is therefore rightfully
dismissed.

~~~
ada1981
I would say that God is exactly what you are studying when you are looking at
dark matter. God is a metaphor for the unknowable ground of being, the mystery
that holds us all. The wisdom traditions have been about understanding the
patterns of the Universe, in all senses and to provide a mechanism and context
to dissolve the idea that something exists as separate from anything else.
Theists and Atheists both seem to get it wrong when they argue over the
"existence" of God, as Joe Campbell said, it's about understanding how to read
a metaphor and experiencing the direct internal subjective experience of
reconnection.

