Germany and US-based astronomers have located a star-forming region on the opposite side of the Milky Way, measuring a distance of 66,000 light-years, almost twice their own record. They used an array of telescopes between Hawaii and the US east coast, taking measurements in six-month gaps, as the Earth moves to opposite sides of the Sun, to pinpoint the location.
For the first time ever, astronomers have pinpointed the location of a luminous light source on the opposite side of the Milky Way Galaxy, far beyond the galactic center. The source — a region of space where massive stars are being born — is located in a distant spiral arm, one of the large tentacles of gas that swirl around the middle of our galaxy. Knowing its location has allowed astronomers to trace the arm as it wraps around the center of the Milky Way, telling us more about the structure of the galaxy we live in.
It’s a significant discovery, since locating distant objects in our galaxy is an incredibly difficult process. The Milky Way is filled with interstellar dust that makes it nearly impossible to see any visible light coming from faraway sources. And our galaxy is incredibly big, stretching 100,000 light-years across. That means it takes a thousand centuries for light to cross from one end of the Milky Way to the other. Any radio waves coming from remote locations across the galaxy weaken considerably as they cross the vast distances on the way to Earth.
That’s why astronomers use special measurement techniques to figure out where things are in our galaxy. To find this specific star-forming region, scientists leveraged the Earth’s orbit around the Sun, observing the source’s radio waves from different vantage points as the Earth travels through the Solar System. Such a technique can help astronomers accurately measure the distance of a far-off object — it’s been used to do so many times before — but a galactic object this far away has never been measured before. “This is certainly the first source we’ve ever measured a distance that far by a factor of two,” Mark Reid, a senior radio astronomer at Harvard and author of a study in Science detailing this discovery, tells The Verge. “So it’s twice as far away as the previous record holder.”
Reid and his team weren’t looking for this light source in particular; they found it as part of an ongoing mapping campaign of the Milky Way. Over the last five years, the team has been measuring the distances of star-forming regions all over the galaxy to learn more about the structure of our cosmic neighborhood. And they’ve located up to 200 sources so far. The team has been looking specifically for these regions — dense clouds of gas and dust that form new stars — because such places are known to pop up in the arms of spiral galaxies. It’s thought that gases within the arms bump up against each and other and become so compressed that they give birth to new stars.
But so far, all of the regions that the team has mapped have been in the general vicinity of our Solar System. They hadn’t found any sources far beyond the galactic center — the supermassive black hole at the middle of the Milky Way. That’s because it’s fairly difficult to map the galaxy from Earth. “Imagine you’re trying to make a map of a city, but you’re not allowed to leave home,” says Richard Pogge, an astronomer at Ohio State University, who wasn’t involved in the study, tells The Verge. “You go and look at distant lights and try to map out where the population of the city is. But up until now we’ve only seen downtown and mapped out a few of the suburbs.”