Astronomers have made a truly historic discovery. In the course of these observations, they found a new millisecond pulsar in the very ancient globular star cluster M15 (NGC 7078). Designated as PSR J2129-1210O, or M15O for short, this pulsar was discovered using the Five-hundred-meter Aperture Spherical Radio Telescope (FAST). It was found during a Great Observatories Combined Sciences campaign from Nov 2019 to Feb 2024.
M15 is located approximately 35,700 light years from Earth. It is well-known for being one of the oldest core-collapsed clusters in the Milky Way, and it is positively bursting with pulsars. The cluster’s rich environment frequently leads to confusing signal overlaps. These overlaps can severely obscure the detection of new pulsars, masking M15O and making it a challenge to identify.
Characteristics of M15O
M15O is quite the remarkable beast, with a spin period of only 11.07 milliseconds. This positions it right at harmonics of the well-studied famous pulsar PSR J2129+1210A, otherwise known as M15A. They found M15O only 0.37 arcseconds from the center of the cluster. It is located 0.81 arcseconds from M15A. Because of this positioning, this makes M15O the closest known pulsar to the optical center of M15.
All the difficult conditions that make M15’s located environment so elusive aided in M15O’s earlier non-detection. Yinfeng Dai, a lead researcher from Guizhou University in China, noted how signal overlaps complicated the identification process:
“If the period of a new pulsar is similar to or overlaps with that of a known pulsar or its harmonics, and their DM [dispersion measure] values are also close (owing to the concentrated DM distribution within the cluster), conventional folding algorithms struggle to separate the signals due to phase—alignment ambiguities. The standard screening process may fail to effectively distinguish between them, potentially leading it to miss the new pulsar,” – Yinfeng Dai et al.
The Importance of M15 and Its Pulsars
Surprisingly, what is M15’s approximate age? It provides unprecedented new understanding of how star clusters like the sun’s form and change in our galaxy. With a large population of pulsars within this intense cluster, it makes the region crucial for astronomers researching neutron stars and their movements or behaviors.
Pulsars such as M15O are invaluable cosmic laboratories. Scientists use them to test theories about gravity, stellar evolution, and high-energy physics. Every new pulsar discovered increases our knowledge of these extremely interesting celestial phenomena. It inspires us to reach even deeper into the mysteries that surround them.
Thrusting into that molecular cloud, Dai and his team made powerful observations that unveiled M15O. Their work underscored the work of advanced radio telescopes such as FAST to further explore deep space phenomena. As technology advances, so does the ability to find these hidden astrophysical treasures.
Future Research and Implications
It is more than just adding another pulsar to the catalog. Most importantly, it shows what’s possible in finding more of the elusive pulsars lurking inside dense populated star clusters. Now, with the recent LIGO data, researchers are honing their methods to separate blended signals. This enhancement increases their capacity to discover new, previously-unsearched pulsars.
Our discoveries concerning M15O should inspire new thinking as we plan our next observational campaigns. These campaigns might be redirected to other globular clusters that have vigorous pulsar populations. Yet astronomers are constantly extending our knowledge of what our universe is and how it operates. Finds from the neighborhood of M15O only encourage more inquiry and research.