May 18, 2022


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Searching for dead stars -

Searching for dead stars –

Neutron stars are small, but of almost incomprehensible density and gravity.

Indeed, they are dead stars, but there is enough life in them to be some of the most exciting stars you can find in space.

Neutron stars aren’t just great for astronomers. They are unique laboratories for extreme physics, says Manuel Linares, a professor at the university physics department in NTNU.

Over the next five years, he will lead a research group that will study and search for neutron stars. The European Research Council (ERC) supports research with an amount of NOK 20 million through a file ERC Consolidator Grant.

Looking for the most massive

The goal is to find some of the most massive neutron stars and understand more about the double stars that we can find as part of them, says Linares.

The professor participated in the development of a new method for measuring the mass of neutron stars. More on that later.

The European Research Council (ERC) is supporting Professor Manuel Linares and exploration with an amount of NOK 20 million through the ERC Consolidator Grant. Photo: Per Henning / NTNU

search process It was named LOVE-NEST. The acronym stands for Searching for Supermassive Neutron Stars, and What Else? Four post-doctoral researchers and four doctoral students are participating.

But what exactly are neutron stars? To explain this, we need to look at what happens when stars die.

The stars live after death

When stars die, there are several possibilities. And no, we’re not talking about better music sales and applauding the obituaries without criticism. We’re still talking about real stars.

Stars die when they somehow use up their fuel. Then some of them explode.

What they become after that depends on how much mass they initially had.

  • Small-mass stars are formed white dwarf stars. Some may continue to shine at low intensity for billions of years afterward. It is possible that this will happen to our sun one day.
  • Some stars with the largest mass become famous black holes, a region in space where gravity is so strong that no light is emitted.
  • But stars that do not have the same amount of mass are created neutron stars instead of. This occurs when the mass at birth corresponds to about 10 to 25 times the mass of our Sun. These neutron stars are very special.
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The large red circle represents the neutron star on the map of London.
Neutron stars are very crowded, but they are small. This is a typical neutron star compared to central London. Illustration: Google Maps and Kolbjørn Skarpnes / NTNU

Neutron stars are small but very densely packed. One cubic meter of the final neutron star could weigh a trillion kilograms. You may not know what that means, but it’s a number followed by 18 zeros, or 1,000,000,000,000,000,000.

For the same reason, the gravitational field of a small neutron star can be 100 billion times stronger than our sun. One number has 11 zeros if you were wondering.

Neutron stars have a greater mass than our Sun, but are usually only about 20 kilometers in diameter, says Professor Linares.

By comparison, our Moon is about 3,500 kilometers in diameter, and Earth is just over 12,700.

Thus it would be impossible to find neutron stars if we only used our eyes to search for them. But we don’t. That’s why we know so little.

Only see some neutron stars


  • If you have a swivel or carousel on the playground, you know that it is much easier to circle a small child than it is to circle a large adult. It’s a bit like that with the stars, too.
  • An ordinary star has a certain rotation or driving moment that causes it to rotate at a certain speed.
  • After the star’s core collapses into a neutron star, it retains roughly the same driving momentum. But due to its small size now, and the torque almost the same, the rotation speed is much higher.
  • Some pulsars can rotate several hundred times per second. The rapidly rotating magnetic field causes the star to create a strong electric field. Then rays of electromagnetic radiation are formed at the poles of the star. This radiation is ejected into space and we can measure it.
  • From a fixed observation point on the globe, the radiation is tested in the form of a pulse pulsing when the poles are moving towards us.
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In our galaxy alone, we know more than 3,000 neutron stars, but many of them are hidden from us, says Professor Linaris.

One reason we know some, but not others, is that some neutron stars turn into pulsars.

These pulsars rotate several times per second. Then electromagnetic radiation is formed, and this radiation can be measured. This way we can know where the star is, even if we don’t see the star itself. (Take a look at the fact box if you want to know more.)

The vast majority of neutron stars that we know of are just such pulsars. Another type is magnetars, where we can observe the effect of ultra-strong magnetic fields, but in this article we will stick to faster-spinning pulsars.

The mass of dead stars must be measured

As if finding tiny, distant neutron stars in the universe wasn’t hard enough, LOVE-NEST also aims to find their masses.

It is possible to measure the mass when a neutron star merges with another star, explains Professor Linaris.

Thus, the pulsar has formed a double star with another star. It is difficult to measure a neutron star by itself, but we can easily measure the effect of a neutron star on another star.

We have developed a new and more accurate technique for measuring the mass of an interesting group of pulsars with great accuracy, says Professor Linares.

The new method uses temperature differences to calculate velocity and mass.

The intense heat affects the companion star

Kelvin and Celsius

  • Physicists often use the kelvin instead of the degree Celsius.
  • Degrees of Kelvin depend on the absolute zero point, which is then equal to exactly 0 K, but it is close to – 273.15 ° C. It couldn’t get any cooler.
  • A change of 1 degree in Kelvin is equal to a change of 1 degree measured in degrees Celsius. Thus water freezes into ice at exactly 0 °C and about 273.15 K.
  • When we talk about millions of degrees, for all practical purposes, most of us don’t matter whether we use Kelvin or Celsius.
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You might think our sun is warm, and so is it, but it settles at around 5700 degrees Kelvin On the surface and just over 14 million inside.

Neutron stars can maintain a temperature of up to 100 million degrees. Of course, these stars don’t do anything halfway.

When an ordinary star and a pulsar orbit a common center of mass, the pulsar will affect the temperature of that companion star, the professor explains. (Watch the movie below).

It can read velocity and mass

The part of the companion star closest to the pulsar is warmer than the other side.

Professor Linares himself noticed this not long ago, as part of his Spanish language work Polytechnic University of Catalonia (UPC)Famous astronomical observatories were used in the Canary Islands.

– This pulsar caused the surface temperature of the companion star to differ by 2,400 degrees, says the professor.

The variation in temperature also changes the chemical spectrum that the tracking star gives off. This spectrum can be measured by physicists even when the two stars are 10,000 light years away from us. (Watch the movie below).

This, in turn, allows us to see how fast the observer is orbiting the pulsar at any given time. When we know velocity, Linaris says, we can also calculate mass.

This pulsar had a mass 2.3 times the mass of our Sun. This is what you should find like these LOVE-NEST neutron stars.

The professor will at least be busy enough to move on, but no worse than sharing his knowledge.

In January, Linares Underestimate “observational astrophysics” For master’s degree students in Physics at NTNU. It’s not impossible for neutron stars to appear in this path either.

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