The Milky Way's shape could actually be normal
There’s more to the Milky Way than meets the eye. The silvery stream that spills across the night sky is just one piece of the complicated bundle of stars that makes up our galaxy. Astronomers have dubbed this pinwheel shape the “thin disk,” which sits inside a fluffier “thick disk” of stars a few times as tall, a bit like the filling inside a Boston cream doughnut.
But where did the two disks come from? Are they a scar from a cosmic childhood trauma, or an inevitable mark of galactic maturity? With just one sample galaxy (our own) to study in detail, astrophysicists and astronomers have struggled to land on one origin story. Now, a new survey has spotted some of the strongest evidence yet for similar disks in a neighboring galaxy. The finding suggests that the Milky Way’s dual disks are a common galactic evolution, not the unique result of some extraordinary past. That confirms our galaxy’s potential as a powerful example for understanding galaxies all over the universe.
“We can take all of these lessons from the Milky Way and apply them to all these other galaxies,” says Jesse van de Sande, an astronomer at the University of Sydney and coauthor of the new research. “But that only works if the Milky Way isn’t special.”
Two tales of two disks
In practice, astronomers separate the two disks of the Milky Way by their composition. The stars of the thin disk are swimming in metals (which, from the peculiar perspective of astronomers, means all elements heavier than hydrogen and helium), while “metals” are rather rare in thick disk stars.
This difference establishes a rough timeline, giving astrophysicists the “when.” Thick-disk stars formed first, directly from the hydrogen and helium gas clouds that choked the young universe. Secondary, thin-disk stars started to form hundreds of millions of years later, after the early generations of stars had time to forge heavier elements and explode, spewing metals in every direction.
But working out the “how” has proven tricky. To get two clear disks, some process must have dramatically slowed star formation throughout the whole galaxy as it transitioned between the era of the first disk and the era of the second disk.
[Related: Meet the disk-shaped halo of hot gas you currently live in]
Two leading theories have emerged. Maybe the young Milky Way smashed into a similarly sized galaxy after the first disk formed, stirring up its gas and dust too much for stars to gravitationally pull themselves together.
Or, perhaps the two disks resulted from two different types of supernovae, each churning out metals in different ways. Early on, so-called “core-collapse” supernovae were the norm because the giant stars that cause them were plentiful. After the galaxy’s big stars popped off, another flavor of supernova (perhaps caused by smaller stars colliding) would have taken over.
The debate has far reaching consequences. Much of what astronomers know about galaxies is based on the Milky Way, since it’s the galaxy they can see most clearly. But if its large-scale features arose from a one-off collision billions of years ago, then researchers have risked basing their theories on a lone, misshapen galaxy.
“If it turns out the Milky Way is unique because of some merger event 8 billion years ago, then that whole picture of using our Milky Way as a template for all other galaxies just falls apart,” van de Sande says.
A galaxy not so far, far away
To find out whether the Milky Way is an oddball, van de Sande and his collaborators pointed the Multi Unit Spectroscopic Explorer (MUSE) of Chile’s Very Large Telescope (VLT) at nine galaxies, all relatively nearby and generally similar to the Milky Way in size and shape. The team was looking for evidence of similar two-disk configurations by looking at the galaxies’ distribution of “metals,” to check if they match what astronomers see in our own double-disk galaxy.
Previous attempts to pick out patterns in metallicity have been inconclusive because most telescopes perceive far off galaxies as single points of light. But MUSE can simultaneously image many thousands of points within a galaxy. “It produces images that are almost as good as Hubble,” says Nicholas Scott, a coauthor also at the University of Sydney.
Seven of their observations were successful, and they set to work analyzing the metal distribution of the galaxy that appears the most edge-on from Earth, figuring that its orientation would help the thin disk pop out from within the thick disk. They were right.
“The first galaxy that we looked at, bam, straight away we got the bimodal star distribution,” or thin and thick disk combo, van de Sande says. The existence of a second two-disk galaxy suggests that the Milky Way is rather vanilla, perhaps because the two types of supernovae naturally produce thin and thick disks in most spiral galaxies. The group published their results May 24 in The Astrophysical Journal Letters.
[Related: The Milky Way could have dozens of alien civilizations capable of contacting us]
The finding is not quite definitive. Not even MUSE can image individual stars in other galaxies, so the metal distribution is more blurred than what astronomers have assembled for the Milky Way. “It’s like [comparing] apples to something almost like apples,” Scott says.
And while two galaxies with disks are better than one, the discovery doesn’t rule out both galaxies experiencing violent collisions while young. Simulations have found that such mashups happen to about 1 in 20 galaxies—rare, but not exceedingly so. To strengthen their result, the astronomers plan to analyze the remaining six galaxies they have data for, and eventually return to the VLT to expand their search. “The next step is to go big on this,” van de Sande says.
For now, astronomers can feel a bit more secure that they likely have a prime view of a very standard galaxy.
“We’ll always know more about the Milky Way than any other galaxy. If we can take that detail and apply it to other galaxies where we have limited data and fuzzy images,” Scott says, “that’s such a powerful tool.”
(责任编辑:资讯)
-
Séamus Malekafzali ,July 23, 2024 Netanyah ...[详细]
-
茂名年货一出手,就承包了你春节的餐桌聚会 | 广东年货大摸底茂名篇_南方+_南方plus茂名是全省农业GDP连续超千亿的地级市荔枝、龙眼、化橘红、罗非鱼、沉香等均居全国第一而且都声名远扬!那茂名有什 ...[详细]
-
隆冬时节,名山区蒙阳街道上瓦村寒风瑟瑟。1月9日,天还未亮,上瓦村9组村民范富荣就抱着一捆青草向兔舍走去。“这小红眼瞪得圆溜溜的,一看就是饿了。”看着一只只等待喂食的兔子,范富荣心里很高兴。在100多 ...[详细]
-
中国山东网青岛3月1日讯随着中产阶级消费群体崛起,厨电行业已开始向高端化转型,消费市场也将迎来新一轮的变革。而作为较早布局国际高端产业的企业,海尔厨电不仅联手美国百年家电GEA探路中国厨房高端升级,推 ...[详细]
-
Eng name ODI, T20I squads for Aus series
England is set to take on Australia at home in September in a three-match T20I series, followed by f ...[详细] -
化妆品进口门槛进一步提高。记者从山东检验检疫局获悉,《进口化妆品境内收货人备案、进口记录和销售记录管理规定》将于3月1日起施行。该规定对进口化妆品境内收货人备案、进口记录和销售记录进行了详细规定,标志 ...[详细]
-
中国山东网青岛2月23日讯2017年开年,卡萨帝洗衣机便在高端洗衣市场呈现出大幅增长之势,相关数据显示,其1月份业绩上涨至113%,同时在月销量方面实现强势翻番,夯实了其作为全球高端家电领头羊的地位。 ...[详细]
-
2017年3月5日,正值第54个学雷锋日,交通银行青岛分行积极响应中国银监会与共青团中央的要求,组织了青岛志愿者与青岛科技大学团委联合开展了“送金融知识进校园”活动,践行雷锋精 ...[详细]
-
Sinner vs. Michelsen 2024 livestream: Watch US Open for free
TL;DR:Live stream Sinner vs. Michelsen in the 2024 US Open for free on 9Now or TVNZ+. Access these f ...[详细] -
瑗挎捣宀告柊鍖?016骞碐DP杩?900浜 鍏ㄥ浗鏂板尯涓夊己
銆€銆€宀佹湯鏂版槬锛岄潚宀涜タ娴峰哺鏂板尯鍐嶆琚仛鐒︼紝浣滀负涓浗鏈€澶х殑閲嶅瀷姹借溅鐢熶骇浼佷笟鐨勪腑鍥介噸姹斤紝灏嗘姇璧?5浜垮厓鍦ㄨ鍖哄缓璁炬柊鑳芥簮鍟嗙敤杞﹂」鐩紝椤圭洰鍏ㄩ儴杈 ...[详细]