This Is (Probably) the Only Way Dark Matter Interacts with Ordinary Matter

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This Is (Probably) the Only Way Dark Matter Interacts with Ordinary Matter

By Harrison Tasoff, Space.com Contributor | April 6, 2018 07:30am ET

                               
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This image shows the four central galaxies in the Abell 3827 cluster with ultraviolet light from the Hubble images (blue) and infrared light from the ALMA observations (red). At these wavelengths, scientists can determine the extent to which a galaxy behind the cluster has been distorted by the gravity of the normal and dark matter.

Credit: RIchard Massey (Durham University)/NASA/ESA/ESO

Dark matter has led scientists on a bit of a wild goose chase lately. New, more accurate measurements of a group of colliding galaxies appear to indicate that the mysterious substance likely interacts with itself and ordinary matter only via gravity, reversing conclusions scientists had drawn from observations three years earlier.

Dark matter accounts for about 27 percent of the universe's contents, but scientists still know very little about what it actually is. It doesn't emit or reflect light, making it very hard to study. Its gravity can, however, bend the path of light in a phenomenon known as gravitational lensing, which has allowed astronomers to ascertain that something is out there.

Three years ago, a team of researchers used the Hubble Space Telescope to observe galaxies colliding in the Abell 3827 cluster, located about 1.3 billion light-years from Earth. The galaxies' dark matter appeared offset from the visible matter in the collision, which the scientists said could indicate that dark matter might feel other forces in addition to gravity. [

The same group of scientists revisited this observation for a new study with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. The powerful telescope was able to pick out details that the Hubble observation hadn't caught: distorted infrared light from a background galaxy. The new data reveal the location of previously undetected dark matter around the collision.

"We got a higher resolution view of the distant galaxy using ALMA than from even the Hubble Space Telescope," Liliya Williams, a researcher at the University of Minnesota and a co-author of the new work, said in a statement. "The true position of the dark matter became clearer than in our previous observations."

The new picture that has emerged indicates that most of the galaxies' dark matter stayed with them during the collision. This suggests that dark matter either exclusively feels the effects of gravity or that it interacts only weakly via other forces.

Alternatively, the cluster could be moving toward Earth, in which case we wouldn't expect to see any sideways displacement in the dark matter, the scientists said in the statement. If this were the case, the dark matter would have shifted either in front of or behind the cluster, making the offset hard to detect. The team will announce their findings on April 6 at the European Week of Astronomy and Space Science conference in Liverpool, England.

Astronomers worldwide continue to look to the sky for clues about the nature of dark matter. In the past few years, many new hypotheses have evolved to explain the substance as scientists use computer models to get a better idea of what to look for. "Different properties of dark matter do leave tell-tale signs," Andrew Robertson, a researcher at Durham University in the United Kingdom and a co-author of the study, said in the statement.

"One especially interesting test is that dark matter interactions [would] make clumps of dark matter more spherical," Robertson added. "That's the next thing we're going to look for."

The new work will appear in the journal Monthly Notices of the Royal Astronomical Society.

Follow Harrison Tasoff @harrisontasoff. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.

这是（可能）暗物质与普通物质相互作用的唯一途径

作者Harrison Tasoff，Space.com撰稿人| 2018年4月6日美国东部时间上午07:30

                               
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该图显示了Abell 3827星团中的四个中央星系，其中来自哈勃图像的紫外光（蓝色）和来自ALMA观测的红外光（红色）。 在这些波长处，科学家可以确定群星背后的星系因正常和暗物质的重力而变形的程度。

来源：RIchard Massey（达勒姆大学）/美国国家航空航天局/欧空局/ ESO

最近，暗物质已经导致科学家们有点疯狂追逐。对一组相互碰撞的星系进行的更精确的测量表明，这种神秘的物质只能通过引力与自身和普通物质相互作用，扭转了科学家三年前观测的结论。

暗物质占宇宙内容的大约27％，但科学家们对它的实际情况知之甚少。它不会发射或反射光线，因此很难学习。然而，它的引力可以通过一种称为引力透镜的现象来弯曲光线，这使得天文学家可以确定有什么东西在那里。

三年前，一组研究人员使用哈勃太空望远镜观测位于距离地球约13亿光年的Abell 3827星团中的星系碰撞。科学家说，星系的暗物质与碰撞中的可见物质相互抵消，这可能表明暗物质除了引力之外还可能感受到其他力。 [

同一组科学家重新审视了这一观察结果，在智利的阿塔卡马大型毫米波/亚毫米波阵列（ALMA）进行了一项新的研究。强大的望远镜能够挑出哈勃望远镜未能捕捉到的细节：来自背景星系的扭曲红外线。新数据揭示了碰撞周围以前未被发现的暗物质的位置。

明尼苏达大学研究员，新作的合着者Liliya Williams在一份声明中说：“我们用ALMA得到了一个更高分辨率的遥远星系的视图，而不是哈勃太空望远镜。” “暗物质的真实位置比我们先前的观察结果更清晰。”

已经出现的新图像表明，在碰撞期间，大多数星系的暗物质都与它们一起存在。这表明暗物质或者只能感受到重力的影响，或者只能通过其他力量弱相互作用。

另外，这个星团可能正在向地球移动，在这种情况下，我们不希望在暗物质中看到任何横向位移，科学家在声明中说。如果是这种情况，那么暗物质就会在集群的前面或后面发生变化，使得偏移很难被发现。该团队将于4月6日在英国利物浦举行的欧洲天文与空间科学周大会上公布他们的发现。

世界各地的天文学家继续向天空寻找有关暗物质性质的线索。在过去的几年中，许多新的假设已经演变为解释实体，因为科学家们使用计算机模型来更好地了解要寻找什么。 “暗物质的不同属性的确会留下迹象，”英国杜伦大学研究员Andrew Robertson和该研究的合着者之一在声明中说。

“一项特别有趣的测试是暗物质相互作用[会]使暗物质团块更加球形化，”罗伯逊补充道。 “这是我们要寻找的下一件事。”

这项新工作将出现在皇家天文学会月刊中。

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