First time history, astronomers have discovered 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.”