Ghost galaxy prompts cosmic mystery

Posted: March 28, 2018 by oldbrew in Astrophysics, research, Uncertainty
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Distant galaxies [image credit: phys.org]


Does the exception prove the rule, or is the rule on shaky ground? Nobody knows.

Scientists have imaged a “transparent” galaxy that may have no dark matter, reports BBC Science.

An unusually transparent galaxy about the size of the Milky Way is prompting new questions for astrophysicists.

The object, with the catchy moniker of NGC1052-DF2, appears to contain no dark matter.

If this turns out to be true, it may be the first galaxy of its kind – made up only of ordinary matter. Currently, dark matter is thought to be essential to the fabric of the Universe as we understand it.

The study is published in Nature.

Ghostly glow
The authors of the study weren’t initially on the hunt for a dark matter-free galaxy; instead they had set out to take a closer look at large, ultra-diffuse galaxies.

These are similar in size to the spiral galaxies we’re more familiar with, but have a fraction of the number of stars.

When Prof Pieter van Dokkum, lead author of the study, first spotted NGC1052-DF2, “I stared a lot at that image and just marvelled at it… It’s like this ghostly glow in the sky.”

The galaxy has very few stars, but many of them are grouped together in unusually bright clusters. When the team studied the behaviour of these clusters, they found that the stars seemed to account for all of the galaxy’s mass.

Leaving no room for dark matter.

Continued here.
– – –
Dark matter is a type of matter which has not yet been directly observedWikipedia

Comments
  1. oldbrew says:

    So something ‘which has never not yet been directly observed’, was not observed 😐

  2. A C Osborn says:

    Not only was it not directly observed, these Galaxies can’t possibly have any.
    OOOOOOPs

  3. ivan says:

    It sounds as if the astrophysicists need to dump their fudge factor of dark matter and look at what is actually there and how gravity interacts in the galaxy.

  4. JB says:

    All this confusion because of Jan Oort’s red-shift dilemma.

  5. HernyM says:

    The link in “The study is published in Nature” does not resolve. Maybe they changed it. Anyway, it is now https://www.nature.com/articles/nature25767

    [reply] thanks Herny – BBC link was wrong

  6. Bitter@twisted says:

    Dark matter is an abstract concept.
    Not surprising it hasn’t been found in the real universe.

  7. oldbrew says:

    Study says:
    Here we report the radial velocities of ten luminous globular-cluster-like objects in the ultra-diffuse galaxy5 NGC1052–DF2, which has a stellar mass of approximately 2 × 108 solar masses. We infer that its velocity dispersion is less than 10.5 kilometres per second with 90 per cent confidence, and we determine from this that its total mass within a radius of 7.6 kiloparsecs is less than 3.4 × 108 solar masses. This implies that the ratio Mhalo/Mstars is of order unity (and consistent with zero), a factor of at least 400 lower than expected. [bold added]

    Quite a headache for dark matter theory…

    DARK, BUT NO MATTER —
    Galaxy seems to lack dark matter, stumping astronomers
    “This thing is astonishing—a gigantic blob that you can look through.”

    In fact, the best fit for the motion of the globular clusters is a galaxy with no dark matter at all

    http://arstechnica.com/science/2018/03/galaxy-seems-to-lack-dark-matter-stumping-astronomers/

  8. Phoenix44 says:

    “The exception that proves the rule…” No, no no!

    It is an odd expression that is constantly misused. But it is as it sounds – a stated exception which proves an unstated rule. For example, in a park “ball games allowed on Sundays”. Allowed on Sundays is the exception, the unstated rule is that ball games are not allowed.

  9. oldbrew says:

    This Galaxy Has Almost No Dark Matter—And Scientists Are Baffled
    If astronomers really have found an “undark” galaxy, it’s a strong clue that dark matter is real.

    http://news.nationalgeographic.com/2018/03/dark-matter-galaxy-gravity-dragonfly-physics-space-science/

    Is it? Sounds like wishful thinking to me.

    Lubos Motl argues:
    thursday, march 29, 2018 …
    Dark matter probably exists because in a galaxy, it doesn’t

    I find it obvious that if a rational person believes that the observation above shows that dark matter and visible matter may separate by the distance comparable to the galactic radius, they may sometimes get separated even more than that, and then they have enough velocity to escape from each other.

    If that’s so, there should be galaxies that contain only visible matter – and those that only include dark matter (but the latter are harder to see because everything is dark in them).

    http://motls.blogspot.co.uk/2018/03/dark-matter-probably-exists-because-in.html

    So rather than absence of evidence not necessarily being evidence of absence, it could be evidence of presence – somewhere else :/

    Again this sounds like holding on to a theory for lack of a better one to turn to.

  10. p.g.sharrow says:

    A Galaxy that has little Mater seems to have little Dark Mater, well DUH !
    The mass/inertia evident is caused by the tension caused by the Mater involved.
    Dark Mater/energy, is the effect of Mater on Aether, just because you can measure or infer an effect does not mean you are examining a thing…pg

  11. blob says:

    It is an interesting paper.

    They derive a dispersion of ~3 km/s for this galaxy:

    The observed velocity dispersion is sigma_obs = 8.4 km s−1,as measured with the biweight estimator (see Methods). This value is much smaller than that in previously studied (cluster) UDGs, and not much higher than the expectation from observational errors alone. Taking the errors into account, we find an intrinsic dispersion of sigma_intr = 3.2(+5.5 −3.2) km s−1. The 90% confidence upper limit is sigma_intr < 10.5 km s−1.

    They expected (apparently according to dark matter theory) a dispersion of ~32 km/s:

    The average velocity dispersion of Local Group galaxies with 8.0 ≤ log(M/M_sol) ≤ 8.6 is 32 km s−1 (dotted curve in Fig. 3a).

    The say MOND predicted 20 km/s:

    For a MOND acceleration scale of a0 = 3.7 x 10^3 km2 s−2 kpc−1 the expected velocity dispersion of NGC1052–DF2 is sigma_M ~ (0.05*G*M_stars*a_0)^1/4 ~ 20 km s−1, a factor of two higher than the 90% upper limit on the observed dispersion.

    So MOND had the better prediction, yet is less supported by this data according to them.

  12. bazmd says:

    The image looks like two galaxies destroyed each-other sometime in the past. Maybe it was two black-holes of equal size that collided, causing mutual annihilation into visible matter leaving no super dense matter around.

    If you think about this, what is the density that mass has to be for light not to escape! this in my opinion is your “dark matter” as for “dark energy” this is just the polarity and enormous polar fields from super dense matter and black-holes…

  13. oldbrew says:

    Scientists detect radio echoes of a black hole feeding on a star
    Signals suggest black hole emits a jet of energy proportional to the stellar material it gobbles up.

    Jennifer Chu | MIT News Office
    March 18, 2018

    Scientists from MIT and Johns Hopkins University have now detected radio signals from the event that match very closely with X-ray emissions produced from the same flare 13 days earlier. They believe these radio “echoes,” which are more than 90 percent similar to the event’s X-ray emissions, are more than a passing coincidence. Instead, they appear to be evidence of a giant jet of highly energetic particles streaming out from the black hole as stellar material is falling in.
    . . .
    “You can do this only with these special events where the black hole is just sitting there doing nothing, and then suddenly along comes a star, giving it a lot of fuel to power itself,” Pasham says. “That’s the perfect opportunity to study such things from scratch, essentially.”

    http://news.mit.edu/2018/scientists-detect-radio-echoes-black-hole-feeding-star-0319