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Map of Milky Way halo reveals dark matter ocean

Astronomers noticed distant stars within the faint halo surrounding our Milky Way galaxy and have now created a map of the halo, the primary of its type of these outermost parts of our galaxy. These new observations, the astronomers said in April 2021, present how the Large Magellanic Cloud – the Milky Way’s satellite galaxy – has created a wake, like a ship crusing by way of calm waters, as it’s touring by way of the halo of the Milky Way. The wake exhibits up as a definite vibrant pathway of stars on the map, telling us that the Magellanic clouds are nonetheless touring of their very first orbit across the Milky Way galaxy. And the wake itself could also be made up of dark matter, dragging the celebs together with it!

The discovery was published within the peer-reviewed journal Nature on April 21.

There are many fascinating issues a few galaxy’s halo. They are faint and laborious to look at, lengthen to massive distances out from the galaxy and are, aside from a number of stars, gasoline and dust, thought to comprise of a considerable amount of dark matter. Dark matter is named “dark” not solely as a result of we all know little about it, however as a result of it doesn’t reveal its existence to us by way of mild, only by way of gravitational interaction with different matter. The video above illustrates how far out from our galaxy’s primary disk the halo stretches, in addition to the pathway – the wake – of the Large Magellanic Cloud touring by way of it.

The new map of the Milky Way’s halo (blue elliptical area) with the disk of the Milky Way galaxy, seen from the facet, overlaid, and with the satellite galaxy the Large Magellanic Cloud within the backside proper (the small one is there too). What is fascinating on this picture are the intense areas of the halo: the decrease one is forming a definite pathway – a wake – behind the Large Magellanic cloud. The prime one is a area of extra stars within the northern hemisphere of the halo. Both of those halo anomalies have been first predicted by pc fashions and have now been observationally confirmed. Image through NASA/ ESA/ JPL-Caltech/ Conroy et. al.

If dark matter certainly does make up a lot of the halo – and all totally different theories on dark matter nature agree on that – a galaxy touring by way of the halo would additionally go away a wake within the dark matter, not solely the celebs. As a NASA/JPL statement described it:

The wake noticed within the new star map is considered the define of this dark matter wake; the celebs are like leaves on the floor of this invisible ocean, their place shifting with the dark matter.

The internal areas of the Milky Way halo have already been investigated intimately, however that is the primary time astronomers have been capable of equally map the outer areas of the halo, together with the wake, at a distance of 200,000 to 325,000 light years from the middle of our galaxy (As a comparability, the seen Milky Way galaxy disk that we’re extra acquainted with has a diameter of about 100,000 mild years, so that is far out).

With a halo being so faint, how do you go about observing it? Although the celebs are extraordinarily sparse within the halo, there are nonetheless some there. The researchers measured 1301 stars positioned on the huge distances of the halo, utilizing information from the European Space Agency’s Gaia mission and NASA’s Near Earth Object Wide Field Infrared Survey Explorer (NEOWISE, which additionally gave identify to the comet of 2020). But precisely pinpointing their distances was one of many main hurdles. So they picked solely a particular type of big stars, a classification that NEOWISE might detect, to get exact distances and create the map.

Part of the workforce behind this analysis had predicted how the dark matter within the Milky Way halo ought to appear like, utilizing pc fashions. So when the observational information confirmed a wake behind the Large Magellanic Cloud and one other greater density area of stars within the northern a part of the halo, this was not totally a shock.

Team member Gurtina Besla at University of Arizona’s Steward Observatory mentioned:

What has been a purely theoretical prediction has now been validated by observational information, offering a compelling argument for the existence of dark matter.

Lead writer Charlie Conroy, professor at Harvard University, described how we are able to be taught extra about dark matter by way of combining mannequin and information, akin to what it consists of:

You can think about that the wake behind a ship might be totally different if the boat is crusing by way of water or by way of honey. In this case, the properties of the wake are decided by which dark matter concept we apply.

Smailing man with glasses and beard in front of greenery.

Charlie Conroy is a professor at Harvard University and the lead researcher of the invention of a wake within the Milky Way’s halo, created by the Large Magellanic Cloud because it orbits across the Milky Way. Image through Harvard University.

Nicolás Garavito-Camargo, a co-author of the research at University of Arizona, defined how this analysis is applies to different galaxies as effectively:

The Milky Way is the one galaxy through which we are able to resolve the celebs and the halo to this stage of element, so it’s our most essential ‘natural laboratory’ through which we are able to research how galaxies work usually. We assume that what we observe right here seemingly applies to comparable galaxies all through the universe.

The Large Magellanic Cloud is a small galaxy rotating across the Milky Way, about 160,000 mild years away from us. It and its smaller companion, the Small Magellanic Cloud (usually abbreviated LMC and SMC, respectively), are clearly seen by the unaided eye from the southern hemisphere, the place they give the impression of being precisely like their namesake; like curious stationary clouds. LMC is predicted to collide with the Milky Way in a distance future, and in essence, this collision has already began for those who take the halo into consideration as part of our galaxy.

Bottom line: Astronomers have created a map of the halo of our Milky Way galaxy – its far outer areas – displaying how the Large Magellanic Cloud has created a wake alongside its traveled path, proof that the satellite dwarf galaxy is just on its very first orbit across the Milky Way. The map gives a solution to be taught extra concerning the nature of dark matter, thought to comprise a big a part of the galactic halo.

Source: All-sky dynamical response of the Galactic halo to the Large Magellanic Cloud

Via University of Arizona

Via Jet Propulsion Laboratory

Theresa Wiegert

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