Astronomers Long Thought That A Peculiar Star System Observed By The European Space Agency’s Gaia Satellite

Strange star system may hold first evidence of an ultra-rare 'dark matter star'

In a distant star system, a sunlike star orbits an invisible object that may be the first example of a 'boson star' made of dark matter, new research suggests.

Astronomers long thought that a peculiar star system observed by the European Space Agency’s Gaia satellite was a simple case of a star orbiting a black hole.

But now, two astronomers are challenging that claim, finding that the evidence suggests something far stranger: Possibly, a never-before-seen type of star made of invisible dark matter. Their research, which has yet to be peer-reviewed, was published April 18 on the preprint server arXiv.

The system itself consists of a sunlike star and, well, something else. The star weighs a little less than the sun (0.93 solar mass) and has roughly the same chemical abundance as the sun. Its mysterious companion is much more massive — around 11 solar masses. The objects orbit each other at a distance of 1.4 astronomical units, about the distance at which Mars orbits the sun, making a complete orbit every 188 days.

Scary Space Stories to Tell in the Dark

The universe is full of dazzling sights, but there’s an eerie side of space, too. Nestled between the stars, shadowy figures lurk unseen. The entire galaxy could even be considered a graveyard, full of long-dead stars. And it’s not just the Milky Way – the whole universe is a bit like one giant haunted house! Our Nancy Grace Roman Space Telescope will illuminate all kinds of spine-chilling cosmic mysteries when it launches in 2027, but for now settle in for some true, scary space stories.

This comic style animation shows the front of the Roman spacecraft with a cartoon eye staring ahead and a lit candle in the foreground. The comic shifts back and forth between two frames with different lighting, making it appear as though the flame is flickering.

Flickering Lights

One of the first signs that things are about to get creepy in a scary movie is when the lights start to flicker. That happens all the time in space, too! But instead of being a sinister omen, it can help us find planets circling other stars.

A faint grid pattern is overlaid on a black background. In the upper-middle, a yellow orb appears to sink into this grid. Lines extend outward from it in every direction. A smaller yellow orb and an even smaller green one pass from the left to the right of the center of the screen together. As they move across, they bend the yellow lines of the farther star's light. A faint green circle in the lower-middle of the screen briefly brightens when all of the objects are aligned in the middle of the screen.

Roman will stare toward the heart of our galaxy and watch to see when pairs of stars appear to align in the sky. When that happens, the nearer star – and orbiting planets – can lens light from the farther star, creating a brief brightening. That’s because every massive object warps the fabric of space-time, changing the path light takes when it passes close by. Roman could find around 1,000 planets using this technique, which is called microlensing.

The mission will also see little flickers when planets cross in front of their host star as they orbit and temporarily dim the light we receive from the star. Roman could find an additional 100,000 planets this way!

Two objects in the foreground of this comic style graphic are each covered in a white sheet with black eyes, giving them a ghostly appearance. The parts that stick out hint at each object's true identity; the smaller Roman "ghost" has a communications antenna sticking out from the top while the Webb "ghost" has its primary mirror poking out of one eye and bits of the sunshield showing out of the bottom edges of the sheet. A jack-o-lantern trick-or-treat basket hangs from one corner of the Webb spacecraft. A swirl of stars decorates the gray background of the image.

Galactic Ghosts

Roman is going to be one of the best ghost hunters in the galaxy! Since microlensing relies on an object’s gravity, not its light, it can find all kinds of invisible specters drifting through the Milky Way. That includes rogue planets, which roam the galaxy alone instead of orbiting a star…

This animation starts with a star-studded sky in which the band of the Milky Way is prominent. A small, dark, circular object grows larger as it moves closer, eventually nearly filling the image. Its close approach reveals it to be a spinning gas giant world, covered in bands of clouds. The animation pans to watch the world fly by. The planet grows smaller as it recedes.

…and solo stellar-mass black holes, which we can usually only find when they have a visible companion, like a star. Astronomers think there should be 100 million of these black holes in our galaxy.

This comic style graphic shows a skeletal Roman spacecraft with a tattered deployable aperture cover on a dark gray background.

Stellar Skeletons

Black holes aren’t the only dead stars hiding in the sky. When stars that aren’t quite massive enough to form black holes run out of fuel, they blast away their outer layers and become neutron stars. These stellar cores are the densest material we can directly observe. One sugar cube of neutron star material would weigh about 1 billion tons (or 1 trillion kilograms) on Earth! Roman will be able to detect when these extreme objects collide.

This infographic shows how the life cycle of stars depend on their mass. At the top left, there is a small, yellow, Sun-like star. An arrow points from it to a slightly larger orange star, and another arrow then points to a very small white dwarf star. Beneath this row, a medium-sized orb labeled "massive star" glows blue. An arrow points from it to a larger orange star, and another points to a tiny white neutron star. The bottom row starts with a large, very massive blue star. An arrow points to an even larger orange star, and another points to a small black hole - a tiny black circle with a faintly glowing ring around it. The bottom of the graphic says "The fate of a star depends on its mass (size not to scale)."

Smaller stars like our Sun have less dramatic fates. After they run out of fuel, they swell up and shrug off their outer layers until only a small, hot core called a white dwarf remains. Those outer layers may be recycled into later generations of stars and planets. Roman will explore regions where new stars are bursting to life, possibly containing the remnants of such dead stars.

Silvery threads form a hexagonal, web-like pattern on a dark gray background in this comic-style graphic. The Roman spacecraft appears to be caught in the web.

Cosmic Cobwebs

If we zoom out far enough, the structure of space looks like a giant cobweb! The cosmic web is the large-scale backbone of the universe, made up mainly of a mysterious substance known as dark matter and laced with gas, upon which galaxies are built. Roman will find precise distances for more than 10 million galaxies to map the structure of the cosmos, helping astronomers figure out why the expansion of the universe is speeding up.