An ancient star, named CWISE J124909+362116.0 (J1249+36), has been observed moving through space at an astonishing speed of nearly 600 km/second (1.3 million mph).
This velocity not only surpasses the galactic escape speed but also makes it one of the fastest stars ever detected in the Milky Way. Identified by citizen scientists through the Backyard Worlds: Planet 9 project, J1249+36 is a rare type of small main sequence star called an L subdwarf, making it one of the oldest in our galaxy.
Discovery and Observations
The star was first detected by volunteers who were exploring data collected by NASA’s Wide-field Infrared Survey Explorer (WISE) mission over the past decade. J1249+36 immediately stood out due to its immense velocity, which is almost three times as fast as the speed of the sun in its orbit around the heart of the Milky Way. The speed of this hypervelocity star is so great that it is likely to escape our galaxy altogether.
Something ‘kicked’ this hypervelocity star racing through the Milky Way at 1.3 million miles per hour (video) https://t.co/rCOAGsogJB pic.twitter.com/GLXQ2Nxjat
— SPACE.com (@SPACEdotcom) June 17, 2024
To delve deeper into the star’s characteristics, University of California, San Diego Professor of Astronomy and Astrophysics Adam Burgasser utilized the W.M. Keck Observatory in Maunakea, Hawaii, to observe its infrared spectrum.
This investigation revealed that the star belongs to the class of the oldest stars in the Milky Way, known as L subdwarfs, which are noted for their low masses and relatively cool temperatures. The spectral data combined with atmospheric models allowed the team to pinpoint J1249+36’s position and velocity through the Milky Way.
Theories Behind the Ancient Star’s High Velocity
The extraordinary speed of J1249+36 has led to several intriguing theories regarding its origin. One hypothesis suggests that the star was once part of a binary system with a white dwarf. In this scenario, the white dwarf would have cannibalistically fed on the stellar material of its companion, J1249+36, until it reached the Chandrasekhar limit of about 1.4 times the mass of the sun.
This accumulation of mass would cause the white dwarf to go supernova, completely destroying itself and propelling its companion at high speeds. Burgasser explains, “In this kind of supernova, the white dwarf is completely destroyed, so its companion is released and flies off at whatever orbital speed it was originally moving, plus a little bit of a kick from the supernova explosion as well.”
Another theory proposed by astrophysicist Kyle Kremer from Caltech involves the star encountering a black hole binary within dense star clusters known as globular clusters. In these clusters, stars are densely packed, and interactions with black holes can result in stars being ejected at high velocities. Kremer’s simulations suggest that such interactions can kick a low-mass subdwarf out of a globular cluster, setting it on a trajectory similar to that observed with J1249+36.
A third, more speculative theory suggests that J1249+36 might not originate from the Milky Way at all. Instead, it could have been ejected from one of the several satellite dwarf galaxies orbiting the Milky Way. This hypothesis would imply that the star’s high velocity is the result of gravitational interactions within these smaller galaxies before it was flung into the Milky Way.
Chemical Composition and Origins
To determine which of these theories is correct, scientists plan to examine the star’s chemical composition in greater detail. The elemental makeup of J1249+36 could provide clues about its origins. For example, stars born in globular clusters have distinct chemical signatures, and white dwarfs going supernova can “pollute” their companion stars with specific elements. By analyzing these chemical signatures, researchers hope to trace the star’s journey and pinpoint the exact cause of its hypervelocity.
Significance of Hypervelocity Stars
The discovery of J1249+36 offers a unique opportunity to investigate hypervelocity stars as a whole. These stars are not only fascinating in their own right but also provide valuable insights into the dynamics of our galaxy and the interactions between stars and other celestial objects.
Understanding these high-speed stars can help astronomers refine models of stellar evolution, binary star systems, and the gravitational influences of black holes.
Burgasser presented the team’s findings at the 244th national meeting of the American Astronomical Society (AAS) in Madison, Wisconsin. The continued study of J1249+36 and other hypervelocity stars promises to shed light on the extreme environments and forces at play in our universe.
