Hubble finds galaxy with no evidence of dark matter


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The uncertainty of science: Using the Hubble Space Telescope astronomers have discovered a nearby galaxy that apparently has little or no evidence of dark matter.

The unique galaxy, called NGC 1052-DF2, contains at most 1/400th the amount of dark matter that astronomers had expected. The galaxy is as large as our Milky Way, but it had escaped attention because it contains only 1/200th the number of stars. Given the object’s large size and faint appearance, astronomers classify NGC 1052-DF2 as an ultra-diffuse galaxy. A 2015 survey of the Coma galaxy cluster showed these large, faint objects to be surprisingly common.

But none of the ultra-diffuse galaxies discovered so far have been found to be lacking in dark matter. So even among this unusual class of galaxy, NGC 1052-DF2 is an oddball.

Van Dokkum and his team spotted the galaxy with the Dragonfly Telephoto Array, a custom-built telescope in New Mexico they designed to find these ghostly galaxies. They then used the W.M. Keck Observatory in Hawaii to measure the motions of 10 giant groupings of stars called globular clusters in the galaxy. Keck revealed that the globular clusters were moving at relatively low speeds, less than 23,000 miles per hour. Stars and clusters in the outskirts of galaxies containing dark matter move at least three times faster. From those measurements, the team calculated the galaxy’s mass. “If there is any dark matter at all, it’s very little,” van Dokkum explained. “The stars in the galaxy can account for all the mass, and there doesn’t seem to be any room for dark matter.”

The galaxy is unusual in many other ways.

The Hubble images also revealed the galaxy’s unusual appearance. “I spent an hour just staring at the Hubble image,” van Dokkum recalled. “It’s so rare, particularly these days after so many years of Hubble, that you get an image of something and you say, ‘I’ve never seen that before.’ This thing is astonishing: a gigantic blob that you can look through. It’s so sparse that you see all of the galaxies behind it. It is literally a see-through galaxy.”

The ghostly galaxy doesn’t have a noticeable central region, or even spiral arms and a disk, typical features of a spiral galaxy. But it doesn’t look like an elliptical galaxy, either. The galaxy also shows no evidence that it houses a central black hole. Based on the colors of its globular clusters, the galaxy is about 10 billion years old. Even the globular clusters are oddballs: they are twice as large as typical stellar groupings seen in other galaxies.

The bottom line here is that we have only circumstantial evidence that dark matter exists, based solely on the fact that in all other measured galaxies, the outer stars rotate much faster than they should. That rotation speed however does not guarantee the existence of dark matter, only that something is causing the fast rotation. And the lack thereof in this galaxy puts a big crimp in the theory that dark matter exists, since the theories that posit its existence almost require it to be present in every galaxy.

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4 comments

  • Orion314

    Dark matter, dark energy, the 21st century label for ghosts , spirits, and hobgoblins….
    Science from the flat earth society..

  • Max

    I agree with your summation.
    They conclude that this galaxy has no dark matter simply because the stars are moving slower. It would appear to me, that it is proof, that “the combined mass of the galaxy itself holds the individual stars in check”. A Galaxy as large as the Milky Way with only 1/200 the mass would necessarily have stars moving much slower or they would be flying into deep space.
    The article says;
    “There is no theory that predicted these types of galaxies. The galaxy is a complete mystery, as everything about it is strange. How you actually go about forming one of these things is completely unknown.” And Yet, irregular galaxies are very common.
    Ah, the uncertainty of science.
    It was thought that matter (galaxies) cannot exist without dark matter. Well boys, it’s back to the drawing board…

  • Localfluff

    There are many proofs of the existence of dark matter (or dark mass, rather). This discovery btw totally kills MOND, modified gravity theory, because it is not general but specific to these galaxies (both the one without any dark mass and the one that consists of it to more than 99%, both recently found).

    One of the proofs of dark matter are the so called bullet clusters. They are dark matter free galaxy cluster pairs that have collided. All ordinary matter decelerated by interaction during the collision while the dark matter went on without taking notice, and left the cluster pair. Maybe something similar has happened to these sparse galaxies? Maybe these freaks were thrown off from galaxy mergers? The more galaxies are studied, the more freaks will be found. The “Backward” galaxy was an example. Out of thousands of known spiral galaxies, only one rotated the other way around relative to the direction of its spirals. But they’ve found more and an explanation for how a merger can cause this effect. Freaks are expected as more is observed, no reason to freak out.

    These are found now because dim galaxies and dwarf galaxies are of great interest to astronomers now, in the quest for how the first galaxies were formed. It is really driven by the expectations on JWST. They want to tie in findings like this with whatever the JWST will discover in the first galaxies that ever formed, as it catches the first photons from “Let There Be Light”.

  • Edward

    Max noted: “And Yet, irregular galaxies are very common.

    The article says: “There is no theory that predicted these types of galaxies. The galaxy is a complete mystery, as everything about it is strange. How you actually go about forming one of these things is completely unknown.

    The galaxy that is the focus of the article is the one that is least mysterious.

    The idea of dark matter is a hypothesis, since no one has yet directly detected such material, they only infer its existence. The galaxy in the article works the way we can model one with the information we have — the verifiable information that we have; the classical model works better than the inferred dark matter model. Dark matter is a hypothetical substance that we speculate is there, because we cannot otherwise explain the mystery of how the other galaxies are observed to work. Thus astronomers tell us that they know that dark matter is there, because without it they can’t explain most of their observations.

    It is sort of like observing a ball floating in the air and inferring that there is an unseen string holding it up.

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