Newly discovered star is moving fast enough to escape the Milky Way

Subscribe to CNN’s Wonder Theory newsletter. Explore the universe with news about amazing discoveries, scientific advances, and more..

CNN
—

New research has found that an object spotted with the help of citizen scientists was moving so fast through the Milky Way that it could have escaped the galaxy’s gravity and reached intergalactic space.

The object is likely a faint red star, traveling at 1.3 million miles per hour (600 kilometers per second). By comparison, the Sun orbits the Milky Way at about 450,000 miles per hour (200 kilometers per second).

If confirmed, the object would be the first known low-mass, hypervelocity star, according to a team of astronomers and citizen scientists whose study has been accepted for publication in Astrophysical Journal Letters.

“There are many more low-mass stars than high-mass stars because star formation favors low-mass objects and higher-mass stars have shorter lifetimes,” said Roman Gerasimov, a co-author of the study and a postdoctoral fellow in the Department of Physics and Astronomy at the University of Notre Dame. “But low-mass stars are harder to detect because they are cooler and less luminous.”

Hypervelocity stars, the first It was hypothesized to exist in 1988. These fossils, discovered in 2005, are already extremely rare, which makes this new discovery “particularly exciting,” he said.

Volunteers participate in a project called Backyard Worlds: Planet 9 The star, dubbed CWISE J124909.08+362116.0, or J1249+36 for short, has been discovered for the first time. Researchers involved in the project are seeking evidence of undiscovered objects or a hypothetical large world, called Planet Nine, in the “solar system’s backyard” beyond Neptune.

Backyard Worlds participants are looking for patterns and anomalies in images and data collected by NASA’s Wide-field Infrared Survey Explorer mission, which mapped the sky in infrared light from 2009 to 2011. (The space agency renamed the mission the Near-Earth Object Wide-field Infrared Survey Explorer in 2013 to monitor near-Earth asteroids and comets before it was shut down for good on Aug. 8.)

The star J1249+36 stood out to citizen scientists looking through the data a few years ago because the star was moving at about 0.1 percent the speed of light, according to the study authors.

“I can’t describe the level of excitement,” study co-author Martin Kabatnik, a citizen scientist from Nuremberg, Germany, said in a statement. “When I first saw how fast it was moving, I was convinced it must have been reported already.”

Subsequent observations with several telescopes helped focus on the object and confirm the discovery.

“This is where the source got really interesting, as its speed and trajectory showed that it was moving fast enough to escape the Milky Way,” Adam Burgasser, lead author of the study and a professor of astronomy and astrophysics at UC San Diego, said in a statement.

At first, the star’s low mass made it difficult to classify, leading astronomers to wonder whether it was a low-mass star or a brown dwarf, a celestial body that is neither a star nor a planet.

Brown dwarfs are more massive than planets but not as massive as stars, and citizen scientists working on the Backyard Worlds project have discovered more than 4,000 of them.

But none of those brown dwarfs were accelerating on a trajectory that would carry them out of the galaxy like Hypervelocity “runaway” stars It has been observed by astronomers in the last two decades.

Astronomers observed J1249+36 using ground-based telescopes, including the W. M. Keck Observatory on Mauna Kea in Hawaii and the University of Hawaii Institute for Astronomy’s Pan-STARRS telescope on Haleakala Volcano in Maui.

Data from the Keck Observatory’s near-infrared spectrometer indicate that the star was an L-subdwarf, or a star with much less mass and a cooler temperature than the Sun. Cool subdwarfs are the oldest stars in the galaxy.

Telescope data show that the potential star has a lower concentration of metals, such as iron, than other stars or brown dwarfs.

By combining data from multiple telescopes, astronomers determined the star’s location and speed in space, allowing them to predict that it will exit the Milky Way at some point.

But questions remain about the true nature of this being.

“I calculated the mass of this object and found that it is about 8% of the mass of the Sun by comparing its observed properties with computer simulations of the evolution of stars. This puts this object at the lower limit of the mass allowed for stars, and it is possible in fact that the mass of the object is slightly less than this limit, which means that the object is not a star but a brown dwarf,” Gerasimov said.

The study authors say that discovering more details about this object could help astronomers determine whether it represents a broader group of high-velocity, low-mass objects that have been subjected to extreme accelerations.

Understanding its exact nature could also help them determine when it will leave the galaxy. Previously, astronomers observed a supermassive black hole at the center of the Milky Way giving a quick kick to a star that will leave the galaxy for good in about 100 million years.

Researchers believe there are two possible scenarios that put J1249+36 on its fast track.

The study team said the star is likely a companion to a white dwarf, the remnant core of a dead star that has expelled gases that serve as its nuclear fuel. In these stellar pairs, if the two stars are close together, the white dwarf will pull mass away from its companion, causing an explosion called a nova. When the white dwarf accumulates too much mass, it will collapse and explode as a supernova.

“In this type of supernova, the white dwarf is completely destroyed, so its companion is ejected and flies away at the same orbital speed it was originally moving at, plus a little kick from the supernova explosion as well,” Burgasser said. “Our calculations show that this scenario works. However, the white dwarf is no longer there and the remnants of the explosion, which likely happened several million years ago, have already dissipated, so we have no conclusive evidence that this is its origin.”

Another possibility is that J1249+36 was in a globular cluster, or a group of closely spaced, spherical stars. Astronomers expect black holes of varying masses to be at the center of such clusters. Black holes can form binary pairs that can eject any star that gets too close.

“When a star encounters a binary black hole, the complex dynamics of this triple interaction can eject that star out of the globular cluster,” Kyle Creamer, a co-author of the study and an assistant professor in the Department of Astronomy and Astrophysics at UC San Diego, said in a statement.

Cramer ran simulations and found that interactions between three objects could knock a low-mass dwarf star out of a cluster and set it on a trajectory similar to that of J1249+36.

“It proves the concept, but we don’t actually know which globular cluster this star belongs to,” Kramer said.

What interests Gerasimov is the idea that the object was ejected from a globular cluster because such clusters contain stars that are more than 13 billion years old.

“The chemical composition and distribution of stellar masses in globular clusters reflect the first steps in the formation and evolution of our galaxy,” he said. “However, almost everything we know about globular clusters comes from studies of their highest-mass members because low-mass stars and brown dwarfs are difficult to observe.”

The James Webb Space Telescope has recently allowed astronomers to identify the first brown dwarfs in a globular cluster that have a mass similar to the object. But so far, there have been too few examples to provide a broader understanding.

“However, the presence of this hypervelocity star, if it is indeed a former member of a globular cluster, opens up a new way to study low-mass cluster members by looking for those that have been ejected and are traveling at high speeds through the Sun’s neighborhood,” Gerasimov said. “Since we were able to find one example, there are likely to be many more to be discovered in the future.”

The researchers said that tracing the path that J1249+36 has taken so far in reverse could reveal a crowded part of the night sky where undiscovered clusters are waiting to be discovered.

Now, scientists hope to learn more clues from the star’s elemental composition, which could help explain how it ended up on a path away from the Milky Way.

When white dwarfs explode, they create heavy elements that can be found around J1249+36. Similarly, stars in globular clusters throughout the Milky Way have distinctive patterns of elements that serve as a label for their origins.

“We are basically looking for a chemical fingerprint that can identify which system this star belongs to,” Gerasimov said.