Astronomers have detected what could be the biggest neutron star to date

Astronomers have identified what could be the most massive neutron star to date.

It's a pulsar, named J0740 + 6620, and the differences in the timing of its pulses allowed its mass to be calculated to 2.14 times that of the Sun, packed in a 30-kilometer star of diameter.

To put this in perspective, the Sun has a diameter of 1.391 million km.

These measurements make J0740 + 6620 the first neutron star on 2 solar masses measured in a confidence interval of 68% and clearly bring it closer to the upper limit of rotating neutron star of 2.3 solar masses calculated the year last on the basis of gravitational astronomy.

And this could lead us to better understand the upper limits of these extreme objects.

Neutron stars are formed from stars that start between about 8 and 30 times the mass of the Sun. In dying, these stars project their outer material into space through a series of thermonuclear explosions, fusing the last pieces of available material into their remaining nuclei.

Once the core has completely burned to become iron, the pressure that keeps it falls and the nucleus collapses, compressing the neutrons until they occupy as little space as possible. The resulting object has the density equivalent to an atomic nucleus.

This is similar to the process that produces a black hole, which occurs with more massive objects; However, no black holes were detected below 5 solar masses.

What happens between the upper limit of the neutron star and the lower limit of the black hole is always a mystery – but a phenomenon on which gigantic neutron stars could enlighten us.

How astronomers have calculated the mass of J0740 + 6620 is really smart – and depends a lot on the properties and orientation of the star from Earth.

J0740 + 6620, located about 4500 light-years away, corresponds to a pulsar of a millisecond. This means that it turns incredibly fast and is tilted so that bright radio wave beams firing from its magnetic poles sweep the Earth at every rotation, at the millisecond scale. (This is what it sounds like transcribed in audio.)

The regularity of these pulses can be used for a variety of applications, but when they have slight irregularities, this can also be very revealing.

The pulsar is in a binary system with a white dwarf, which brings us to the second piece of the puzzle: the system is on the periphery of the Earth, so the white dwarf passes between us and the pulsar – what is it? a transit is called.

The way in which the severity of the white dwarf slightly disturbs the regularity of the impulses is such that an astronomical team led by Thankful Cromartie of the University of Virginia, the National Radio Astronomy Observatory, has measured the mass of the pulsar.

(Yukterez / Wikimedia Commons)

This disturbance is called the Shapiro Delay (animated above) and it occurs when the path of pulsar light is curved by the gravity of the white dwarf, which takes a little longer to get to Earth when the white dwarf passes between us and the pulsar. And we hear slightly – the difference is only 10 million seconds.

Cromartie and his team combined five-year survey data with two dedicated observation campaigns and were able to determine the precise timing of the delay. This allowed them to determine how much the gravity of the white dwarf weighed in the space-time, which also allowed him to infer the mass of the white dwarf.

Once the mass of an object in a binary system is known, calculating the mass of the other object is a simple process, returning a mass of 2.14 + 0.10 to 0.09 M⊙ in the credibility interval of 68.3%.

We do not really know how massive a neutron star can be. The commonly quoted figure is 3 solar masses, but the truth is that none has been detected on 2.5 solar masses.

The most massive neutron star could be PSR J2215 + 5135, a pulsar with a mass estimated at 2.27 solar masses, measured with magnesium lines; or PSR B1957 + 20, with an estimated mass as high as 2.4 solar masses, based on the radial velocity deduced from the spectra. The team noted that these two methods are less reliable than the accuracy offered by radio synchronization.

There is also the PSR J0348 + 0432, a little less massive, with 2.01 solar masses, also calculated using the Shapiro delay.

Whether or not this last pulsar is the most massive neutron star to date, research will not fail to tell us more about these enigmatic stars.

"Neutron stars are as mysterious as they are fascinating," said Cromartie.

"These city-sized objects are essentially ginormal atomic nuclei, they are so gigantic that their interiors take on strange properties, find the maximum mass that physics and nature will allow us to learn a lot about this domain." otherwise inaccessible in astrophysics. "

The search was published in Nature Astronomy.