Measuring distance in space is difficult. Unless you know how bright something is inherently, calculating how far away it is becomes a bit complicated.
But knowing the distance can make a big difference in how you interpret your data. It is not unheard of for astronomers to have to revise their findings based on new distance measurements of an object.
What’s unusual is that it happens with something that humans have been staring at for thousands of years. Astronomers have just made a shocking discovery about one of the most well-known objects in Earth’s sky. A new analysis suggests that the Small Magellanic Cloud is not one small galaxy orbiting the Milky Way, but two.
Why do we make this mistake? A team led by astronomer Claire Murray of the Space Telescope Science Institute argues that two separate groups of stars overlap along our line of sight. Their data suggests that the tailmost star cluster hangs out about 16,000 light-years farther than the others.
Findings were accepted astrophysical journal and uploaded to preprint resources arXivmakes a convincing case for the dual nature of what we have hitherto interpreted as a single object.
The Small Magellanic Cloud is one of several dwarf galaxies that orbit (and are slowly incorporated into) the Milky Way.it is 200,000 light years awayaround it 7,000 light years in diameter, the mass of the Sun is approximately 3 billion. It is also paired with another galaxy that appears near the sky, the Large Magellanic Cloud, which is about twice the size of the Small Magellanic Cloud. The two orbit each other as they orbit the Milky Way.
In fact, there have been hints that the Small Magellanic Cloud may not be what it seems. Introduced since the 1980s. The way the star mist moves seems strange. The interstellar gas environment does not seem to be consistent with other properties of the dwarf galaxy, and there appear to be at least two distinct populations of stars within it.
Previous studies had thought that the Small Magellanic Cloud might be strange because it was gravitated to destruction by interaction with the Large Magellanic Cloud, but the shape and dynamics of dwarf galaxies are definitive. It wasn’t.
Murray and her colleagues conducted a thorough investigation of the cosmic cloud to try to understand it thoroughly.They studied data from gaia surveyis a project that maps the three-dimensional positions and velocities of stars in the Milky Way with the highest precision ever. And they used data from a galaxy survey conducted using the. australia square kilometer array The Pathfinder radio telescope will study in detail the composition of the gases that fill the Small Magellanic Cloud in the space between stars.
Their study found that the Small Magellanic Cloud consists of two distinct populations of stars with similar gas masses separated by a significant distance. Each population has its own interstellar gas signature, and the way stars move within each one is different.
The closer of the two clusters is about 199,000 light-years away, according to the researchers’ measurements. The more distant one is 215,000 light years away, a difference equivalent to almost half the distance between the Sun and the center of the Milky Way. The researchers say this is broadly consistent with previous estimates of the Small Magellanic Cloud’s line-of-sight structure, but it’s also the most convincing evidence to date.
The reason we haven’t been able to tell them apart reliably until now is that one is located directly behind the other along our line of sight, almost (though not quite) like a cluster of stars in the night sky. Because it’s close enough that you can see it.
The Small Magellanic Cloud is a well-known and beloved feature of the southern sky. It has been observed for at least thousands of years by indigenous astronomers in Australia, South America, and Africa.
And together with its big brother, it will continue to shine in the sky for many years to come. But its end is imminent. Like many other galaxies before it, it is gradually falling into the Milky Way. This is an important part of how galaxies grow slowly over billions of years.
Thanks to the Magellanic Clouds, we have a front row seat to watching this process unfold.
This study was accepted by astrophysical journalavailable in arXiv.