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Galactic gas can help unveil what dark matter is made of

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The search for dark matter – an unknown and invisible substance thought to make up the vast majority of matter in the universe – is at a crossroads. Although it was proposed nearly 70 years ago and has been searched for intensely – with large particle colliders, detectors deep underground, and even instruments in space – it is still nowhere to be found.

But astronomers have promised to leave “no stone unturned” and have started to cast their net wider out into the galaxy. The idea is to extract information from astrophysical objects that may have witnessed chunks of it as they were passing by. We have just proposed a new method of doing so by tracing galactic gas – and it may help tell us what it’s actually made of.

Physicists believe that dark matter has a propensity to structure itself into a hierarchy of haloes and subhaloes, via gravity. The masses of these clumps fall on a spectrum, with lower mass ones expected to be more numerous. Is there a limit to how light they could be? It depends on the nature of dark matter particles.

[Read: What audience intelligence data tells us about the 2020 US presidential election]

Warm versus cold

Dark matter cannot be seen directly. We know it exists because we can see the gravitational effects it has on the surrounding matter. There are different theories about what dark matter may actually be. The standard model suggests it is cold, meaning it moves very slowly and only interacts with other matter through the force of gravity. This would be consistent with it being made up of particles known as axions or WIMPS. Another theory, however, suggests it is warm, meaning it moves at higher speeds. One such particle candidate is the sterile neutrino.

Image of the Milky Way galaxy with a dark matter halo around it.
Artist’s impression of the expected dark matter distribution around the Milky Way, seen as a blue halo. ESO/L. Calçada, CC BY-ND

If dark matter is cold, a Milky Way-type galaxy could harbor one or two subhaloes weighing as much as 1010 Suns, and most likely hundreds with masses of around 108 Suns. If dark matter is warm, haloes lighter than around 108 Suns cannot form easily. So tallying light mass dark haloes can tell us something about the nature of dark matter.

Halo imprints

We believe that the existence of lower mass haloes can be revealed by carefully planned observations. Astronomers have already got pretty good at this game of hide and seek with dark matter haloes and have devised observations to pick up the damage they leave behind.

A galaxy cluster with dark matter mapped in blue and bright X-rays in pink. Smithsonian/wikipedia, CC BY-SA

To date, observations have targeted mostly the changes in the distribution of stars in the Milky Way. For example, the Large Magellanic Cloud, a smaller galaxy orbiting ours, seems to have a dark matter halo which is massive enough to trigger an enormous wake – driving the stars from across vast regions to move in unison.

A few of the smaller dark matter haloes thought to be whizzing inside the Milky Way may occasionally pierce through large stellar features, such as globular clusters (spherical collection of stars), leaving tell-tale gaps in them. Dark matter haloes can also affect how light bends around astrophysical objects in a process called gravitational lensing.

But the signals left in the stellar distributions are weak and prone to confusion with the stars’ own motions. Another way to probe the effect of haloes is by looking at the galactic gas it affects. Galaxies have plenty of hot gas (with a temperature of around 106 degrees Kelvin) which extends out to their edge, providing a wide net for catching these dark matter haloes.

Using a combination of analytical calculations and computer simulations, we have shown that dark haloes heavier than 108 solar masses can compress the hot gas through which they are moving. These will create local spikes in the density of the gas, which can be picked up by X-ray telescopes. These are predicted to be minute, of the order of a few percent, but they will be within the reach of the upcoming Lynx and Athena telescopes.

Our models also predict that the spikes in the density of the cooler galactic gas (with a temperature of around 105 K) will be even more significant. This means that the cooler gas can record the passage of dark matter haloes even more sensitively than the hot gas.

Another promising way of observing the dark-matter-induced fluctuations in the gas is via the photons (light particles) from the cosmic microwave background – the light left over from the Big Bang. This light scatters off the highly energetic electrons in the hot gas in a way that we can detect, providing a complementary approach to the other studies.

Over the next few years, this new method can be used to test models of dark matter. Regardless of whether dark matter haloes below 108 solar masses are found in the numbers predicted or not, we will learn something useful. If the numbers match up, the standard cosmological model would have passed an important test. If they are missing, or are far fewer than expected, the standard model would be ruled out and we’ll have to find a more viable alternative.

Dark matter remains a mystery, but there’s a huge amount of work going into solving it. Whether the answer will come from instruments on Earth or astrophysical probes, it will no doubt be one of the most important discoveries of the century.The Conversation

This article is republished from The Conversation by Andreea Font, Astrophysicist, Liverpool John Moores University under a Creative Commons license. Read the original article.

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Keep That Hotdish Hot With 65% Off a Luncia Casserole Carrier, Only $11 With Promo Code

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Best Home DealsBest Home DealsThe best home, kitchen, smart home, and automotive deals from around the web, updated daily.

Luncia Double-Decker Dish Carrier | $11 | Amazon | Promo code SDDU9S7F

It has been a long time since the days we could safely have a potluck or other gatherings, but we have a fantastic deal perfect for once those times return. These double-decker Luncia dish carriers can be had for 65% off when you add promo code SDDU9S7F at checkout and clip the coupon on the site (it’s just below the price). These holders fit 9″x 13″ sized baking dishes.

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That means you can insulate and keep two dishes of food warm for only $11 instead of $30. What’s more, your Luncia carrier will arrive by Christmas if you order today as a Prime member.

Just add promo code SDDU9S7F and clip the 5% off coupon to bring the price down to $11 for the blue or the grey option.

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Grab this offer while it’s still around!


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Conquer Your Pup’s Dander and Fur With $700 Off a Cobalt or Charcoal Bobsweep PetHair Plus Robot Vacuum

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Best Home DealsBest Home DealsThe best home, kitchen, smart home, and automotive deals from around the web, updated daily.

Bobsweep PetHair Plus Robot Vacuum & Mop (Cobalt) | $200 | Best Buy

Bobsweep PetHair Plus Robot Vacuum & Mop (Charcoal) | $200 | Best Buy

Allergies can be bad enough as the seasons change. Don’t let pet hair and dander add to that by vacuuming it up early and often. That chore is easier said than done— unless you have a robot vacuum to do the work for you. This lovely bright cobalt Bobsweep PetHair Plus robot vacuum and mop, only $200 today at Best Buy seems like an ideal option. That’s a whopping $700 off, by the way.

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You can get the same deal for the charcoal version of the robot vac, too. This model is not only specially made for picking up pet hair, it self docks and charges when it’s finished with the work.

It also comes with a mop attachment, so it can take care of those kitchen floors for you as well. Grab it while it’s still available for this fantastic price!

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Apple will replace AirPods Pro for free with faulty noise cancellation, static or crackling

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Today, exactly one year after Apple first launched the AirPods Pro — and thus the same day the very first AirPods Pro owners will see their one-year warranties expire — Apple has launched a repair program that offers free repairs or replacements for another whole year if your AirPods Pro experience issues with noise cancellation or static.

Specifically, Apple will fix:

Crackling or static sounds that increase in loud environments, with exercise or while talking on the phone

Active Noise Cancellation not working as expected, such as a loss of bass sound, or an increase in background sounds, such as street or airplane noise

Apple says only a “small percentage of AirPods Pro” are affected by the issues, but it apparently wasn’t just an early batch — Apple says affected units were manufactured “before October 2020,” meaning every AirPods Pro ever made might be eligible. That’s quite a recall if so. Apple says it will repair faulty AirPods Pro for two years after you first buy them.

We’ve heard complaints about degraded noise cancellation before, and at least one Verge editor has replaced their AirPods Pro under warranty. It’s nice to hear that Apple isn’t just cutting buyers off as soon as that warranty expires.

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