Watch That Space!

chandra x-ray observatory (NASA image)NASA is about to make an exciting announcement, apparently. On Monday 21st August there will be a press conference, and there will be actual information (they say) at several places mentioned in this link.

I have not the slightest idea of the details of the announcement [but see update below], except that the title of the page is “NASA Announces Dark Matter Discovery”! It concerns observations with NASA’s Chandra X-ray Observatory. The Chandra site says “Astronomers will announce how dark and normal matter have been forced apart in an extraordinarily energetic collision at 1 p.m. EDT Monday, Aug. 21.”, so I infer from this that they might not have completely pinned down the nature of the Dark Matter so much as found a completely new kind of smoking gun pointing to its existence.

On the other hand, the fact that they might have seen a real physical event suggests that there will be a lot more data about what Dark Matter’s nature might be. So I’m excited. You should be too. Be aware that we don’t know what about 83% of the matter in our universe is made of, except that we’re pretty sure that most of it is not the ordinary stuff contained in our list of known matter types, but something more “exotic”.

So maybe this announcement is about a significant chunk of the Dark Matter, or maybe a less significant and less exotic chunk. I don’t know. But it’s not every day you get to find out what a large amount of the matter in your universe might be made of.

So watch that space (or those spaces), for the results of watching, er …. space, if you get my meaning.

This could be exciting.

[Update 2: There seems to have been a leak! See the first comment! I’ve put the key information here. We shall see on Monday….]


(Spotted at Elron’s View From The Edge.)

(Update 1: Sean of CV probably has more of the inside scoop -see here– so maybe more over there on Monday.)

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15 Responses to Watch That Space!

  1. Anonymous says:

    Somebody posted spoilers at Slashdot. (It also came up during a meeting today, and a team member confirmed the spoilers are broadly correct.)

  2. Clifford says:

    Anonymous:- Thanks! That is very interesting…. I also must remark that slashdot is a really really scary place. This is the first time I’ve ever gone there.

    Anyway, to save people the need to wade through a lot of the scary chatter, here is what the spolier said:

    They’re referring to the Bullet Cluster. It’s a merging system where a small cluster is passing through a large cluster leaving a shockwave that looks like a bullet’s wake, hence the name.
    Dark Matter is collionless, i.e. the DM from the smaller system hasn’t been slowed down by the collion and just zooms through. The gas is slowed down. So, the DM and gas are no longer in the same place. We can see the gas in an X-ray telescope (Chandra) and detect the mass by the gravitational lensing effect on the background galaxies.
    This is the first time that this has been shown, and it basically disproves the entire category of theories that DM is an illusional caused by us not understanding the action of gravity at long ranges (MOND).

    Abstract from a conference talk about this. [] (PDF)

    Interesting stuff. The abstract says:

    Dark matter and the bullet cluster

    M. Markevitch (1), S. Randall (1), D. Clowe (2), A. Gonzalez (3), M. Bradac (4)

    (1) Harvard-Smithsonian Center for Astrophysics, (2) University of Arizona, (3) University of Florida, (4) KIPAC, Stanford University

    1E0657-56, the “bullet cluster”, is a merger with a uniquely simple geometry. From the long Chandra X-ray observation which revealed a classic bow shock in front of a small subcluster, we can derive the velocity of the subcluster and its direction of motion. Recent accurate weak and strong lensing total mass maps clearly show two merging subclusters, including the host of the gas bullet seen in X-rays. This cluster provided the first direct, model-independent proof of the dark matter existence (as opposed to any modified gravity theory) and a direct constraint on the self-interaction cross-section of the dark matter particles. I will review these and other related results.

    This is great stuff!


  3. Evil Old Slashdot User says:


  4. Clifford says:

    See what I mean? 🙂


  5. anon. says:

    Real information from Slashdot? That’s a first.

    Over at Uncertain Principles, Steinn Sigurdsson linked a paper (Markevitch constraining the dark matter self-interaction cross section from this object, and raised an interesting question that I will repeat in the hope that someone here can answer:

    Does anyone know if it’s possible that the new data allow an actual measurement of this cross section?

  6. Levi says:

    The short paper at the link below seems to be very much on topic:

    This would really be the end of MOND, wouldn’t it?

    Does anybody have advance word on whether the dark matter is collisionless or not?

  7. Count Iblis says:

    The dark matter density is pretty low in these clusters. So, “collisionless” is still compatible with pretty large cross sections.

  8. Aaron F. says:

    Oh maaaaaan! I totally called it! The moment I read “dark and normal matter have been forced apart in an extraordinarily energetic collision,” I thought, “that sounds like the bullet cluster!” If only I had posted a time-stamped comment about it before the spoiler came out… 🙂

  9. Count Iblis says:

    Does the gas account for most of the baryonic mass? If not then I don’t see how this disproves MOND.

  10. Brad Holden says:

    To answer the Count’s question, yes the majority of baryons are in the gas. The usual fraction is 85 or so percent with the remainder in stars. Why that changes the conclusions about MOND versus other stuff, I do not understand.

  11. Pier Stefano Corasaniti says:

    I am not an expert of dark matter and halo model at all as I spend most of my time thinking to the dark side of the energy, but what I understood from the abstract I might speculate that the evidence they are claiming would come from the fact that the center of mass of the X-ray images may not coincides with that inferred from the weak and strong lensing analysis. This is because while the gas has been slowed down by the shock, the dark matter particles (which interact only gravitationally) may have continued their motion causing a displacement of the clustered mass, hence a lensing signal which would not be compatible with the position of the baryons. Presumably it might require a very weird theory of gravity to allow baryons to produce a lensing mirage somewhere else with respect to the center of their mass distribution…but it is just my speculation..very interesting stuff indeed.

  12. Jeff Booth says:

    Listening to press conference online right now. Above has a link to images and the paper and the real audo file. Peir Stefano above got the interpretation spot on (bravo!).

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