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An unseen “bullet” a million times the mass of the sun recently blasted an enormous hole in our galaxy’s longest stellar stream, sometimes called the Milky Way’s halo. Using the most detailed 3D map of our galaxy, Ana Bonaca from the Harvard-Smithsonian Center for Astrophysics discovered evidence for the giant “impactor” that plunged through the stellar stream called GD-1.
It was a recent, close encounter with something as yet unknown.
Several stellar streams are moving through our galaxy. They are parades of stars passing through the solar system on a path created after the Milky Way gobbles up a dwarf galaxy and the stars are blasted away from the clusters in the impact.
The researcher is not certain what the enormous object was since there are no obvious signs of it now, but whatever it was, it was epic in proportions.
“It’s much more massive than a star,” Bonaca told LiveScience. “Something like a million times the mass of the sun. So there are just no stars of that mass. We can rule that out. And if it were a black hole, it would be a supermassive black hole of the kind we find at the center of our own galaxy.”
Since there are no signs of an object that caused the hole, or perturbation, in the stream, one possibility is that the object was made of the mysterious substance called dark matter, thought to make up as much as 27 percent of the universe. It exerts a gravitational force on other matter yet remains totally invisible, reflecting no light.
Finding the giant path of a globular “bullet” of dark matter could provide the perfect opportunity for scientists to find out more about it. Physicists believe that dark matter holds galaxies together, and particularly dwarf galaxies that are torn to shreds in galactic collisions, producing stellar streams like GD-1.
"I think this is the first direct dynamical evidence for the small-scale [structure] of dark matter," says CCA's Adrian Price-Whelan. The evidence @adrianprw references is two small breaks & a spur in the GD-1 stellar stream. Read more on @SmithsonianMag: https://t.co/VcTVzJTaUF pic.twitter.com/oVOaXNpe0S
— Flatiron CCA (@FlatironCCA) March 12, 2019
LiveScience previously reported that a stellar stream called S1, the nearest to Earth, is carrying a large amount of dark matter that originally held together a long gone dwarf galaxy. Researchers gave the dark matter in the stream a somewhat frightening name: “dark matter hurricane.”
Why would it seem frightening? Because the hurricane may be headed right for our planet. Fortunately, even though the dark matter is on a collision course with everything we know, it is thought to be perfectly harmless. The hurricane may also help scientists discover more about what it actually is.
“…that hurricane is not going to kill you. Or blow the door off your house. But it just may cause some local spikes in dark matter, which would help researchers hunting dark matter actually find the stuff, the researchers wrote.”
On the other hand, if dark matter caused the enormous hole in the GD-1 stellar stream, then who knows really what it can do? We don’t actually know that the hole was created by dark matter, so it remains a galactic mystery for now. The researchers can’t rule out a second black hole in our galaxy but so far there is no trace of it.
So far, devices that can detect dark matter have not worked, although we know more than ever that it’s there and plays a critical role in our universe.
Rafi Letzter for LiveScience described the “hurricane” like this:
“…a dense cloud of dark matter from a dead galaxy blasting invisibly through us as it follows the remaining stars on their doomed parade.”
Enjoy your day as you contemplate a hurricane of unknown matter passing by you as you read this. The universe remains full of mysteries and they are all around us.
Watch Ana Bonaca discuss dark matter and stellar streams below:
Featured image: Screenshot via YouTube