Level 1 — Absolute Beginner

Astronomers found two dead stars that go around each other. They are called neutron stars.

The pair is very light for this kind of system. Together they weigh about 2.5 times as much as our Sun.

The two stars circle each other in only 2.36 hours. A huge radio telescope in China, called FAST, found them.

star

A big ball of hot gas in space.

neutron star

A very small, very heavy dead star.

Sun

The star at the center of our solar system.

pair

Two things together.

circle

To go around something.

telescope

A tool for seeing far away.

radio

A kind of wave used by telescopes.

hour

Sixty minutes.

Level 2 — Elementary

Astronomers using China's FAST radio telescope have found the lightest pair of neutron stars ever seen. The system is named PSR J1856-0039. Together the two stars weigh about 2.49 times as much as the Sun.

One star is a pulsar, a neutron star that sends out beams of radio waves as it spins. It weighs about 1.30 times the Sun. Its partner weighs about 1.19 times the Sun, which makes it one of the lightest neutron stars known.

The two stars orbit each other every 2.36 hours, the second shortest orbit among confirmed pairs of this kind. Their orbit is slowly getting smaller, just as Einstein's theory of general relativity predicts. The results were published in the journal Physical Review Letters.

pulsar

A neutron star that sends out regular pulses of radio waves.

beam

A narrow line of light or waves.

spins

Turns around quickly.

partner

One of two things that go together.

orbit

The path one object takes around another.

confirmed

Proven to be true.

predicts

Says what will happen before it happens.

general relativity

Einstein's theory of gravity.

Level 3 — Intermediate

Astronomers using the Five-hundred-meter Aperture Spherical Telescope, or FAST, in China have identified the lowest-mass double neutron star system known. Designated PSR J1856-0039, the pair has a combined mass of about 2.49 times that of the Sun, with the pulsar at roughly 1.30 solar masses and its companion at about 1.19, one of the smallest neutron-star masses measured.

The system was first picked up by FAST on May 4, 2020, and follow-up timing has since allowed the researchers to measure the stars' masses with remarkable precision. The two objects circle each other in just 2.36 hours, the second shortest orbit among confirmed double neutron star systems.

Because the stars are so close, they offer a natural laboratory for testing Einstein's general theory of relativity. The team found that the orbit is shrinking at the rate the theory predicts as the system radiates gravitational waves, adding another successful test to a long list. The work appeared in Physical Review Letters.

Systems like this matter because they hint at how neutron stars are born. A very light companion suggests that some of them form through gentler stellar explosions than the more massive examples, a clue that helps astronomers understand the deaths of stars.

designated

Officially named.

combined mass

The total mass of two or more objects.

solar mass

A unit equal to the mass of the Sun.

timing

Careful measurement of when pulses arrive.

precision

The quality of being very exact.

laboratory

A place for experiments.

gravitational waves

Ripples in space and time.

companion

A second object that travels with another.

Level 4 — Advanced

Astronomers using China's FAST radio telescope have reported the lightest double neutron star system yet discovered. PSR J1856-0039 carries a total mass of about 2.49 solar masses, with the pulsar at 1.304 and its companion at 1.185, among the lowest neutron-star masses ever measured and a tight constraint on how such objects can form.

First detected on May 4, 2020, the system has been timed with enough precision to pin the masses to within roughly two hundredths of a solar mass. Its 2.36-hour orbit is the second shortest among confirmed double neutron stars, a compactness that makes relativistic effects unusually easy to see.

Those effects behave as Einstein predicted. The orbit is contracting at the rate expected if the pair is shedding energy as gravitational waves, so the system doubles as a precision test of general relativity in a regime of strong gravity. The results appeared in Physical Review Letters.

The more profound payoff lies in stellar evolution. Double neutron stars are the survivors of two supernovae, and a very light companion bears on how gentle the second explosion can be. Each additional low-mass system narrows the range of plausible formation channels, which is why a single object this unusual is worth a paper.

constraint

A limit that narrows possibilities.

compactness

The state of being tightly packed.

relativistic

Involving effects described by relativity.

contracting

Becoming smaller.

regime

A set of conditions under which something operates.

supernovae

Explosions that end the lives of some stars.

evolution

Gradual change over time.

formation channels

The routes by which an object can come into existence.