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Toward the center of our Milky Way galaxy, in the constellation Sagittarius, astronomers discovered 10 monstrous neutron stars. These particular stars, called pulsars, live together in the globular cluster Terzan 5, a crowded home to hundreds of thousands of different types of stars.

The article was published in Astronomy and astrophysics.

Pulsars are millions (or even billions) times more dense than other stars and spin rapidly, emitting bright pulses of light from their strong magnetic fields, making them a beacon for astronomers to find. In one of the busiest places in our Milky Way, many pulsars in Terzan 5 have evolved into strange and eccentric shapes.

Astronomers already knew that 39 pulsars called Terzan 5 home. With the teamwork of the US National Science Foundation’s Green Bank Telescope (NSF GBT) and the South African Radio Astronomy Observatory’s MeerKAT telescope, 10 more were added to the number.

“It is very unusual to discover new exotic pulsars. But what’s really exciting is the wide variety of such oddities in one cluster,” said Scott Ransom, a scientist at the US National Science Foundation’s National Radio Astronomy Observatory (NSF NRAO). The discoveries were made by an international team of astronomers from the NSF NRAO, the Max Planck Institute for Gravitational Physics (Albert Einstein Institute) (AEI), and the Max Planck Institute for Radio Astronomy.

The Meerkat telescope was able to determine the approximate location of each pulsar by tracking and timing how fast they spin, matched with twenty years of Terzan 5 observations made by the NSF GBT, which revealed the strange and eccentric details of these stars.

“Without the NSF Green Bank telescope archive, we would not have been able to characterize these pulsars and understand their astrophysics,” adds Ransom. NSF GBT archival data allowed astronomers to determine the position of pulsars in the sky, measure their specific motions, and see how their orbits change over time.

Among the findings, astronomers saw two likely neutron stars orbiting each other as a binary system. Of the 3,600 known pulsars in the galaxy, only 20 have been identified as binary binaries of neutron stars.

When pulsars pair up in binaries, the gravitational pull of one on the other can steal material and energy, causing one to spin even faster, becoming a millisecond pulsar. This pair could be a record-breaker, with a new contender for the fastest-spinning pulsar in a binary neutron star system and the longest orbit of its kind. The current record holder for the fastest spinning pulsar already resides in Terzan 5. Only future observations will reveal the truth.

Astronomers also observed three new rare pulsar “spider” binaries (in addition to the five already known in the cluster), called Red Backs or Black Widows, depending on the types of companion stars they have. A companion star falls into the orbit of a spider pulsar, where a web of plasma fills the space between the two (caused by leakage from the companion star due to the pulsar’s energy), slowly dissolving the companion over time.

The discovery of these strange pulsars allows scientists to better understand globular clusters, neutron stars, and even test Einstein’s theory of general relativity, along with expanding what is known about pulsar categories. The research team is already making plans to discover even more at Terzan 5 with the support of volunteers.

Citizen scientists who would like to share in the excitement of this discovery can help at Einstein@Home. This project, led by AEI scientists, has already discovered more than 90 new neutron stars.