General, Research, Technology

Boomerang Nebula: colder than the void of space itself

Wherever you go in the universe, everywherethere will be heat sources. The farther you are from them all, the colder. At a distance of 150 million kilometers from the Sun, the Earth maintains a modest temperature of 26-27 degrees Celsius, which would be 50 degrees cooler if we had no atmosphere. Even further - and the Sun will heat objects less and less. Pluto, for example, at -229 degrees Celsius: cold enough for liquid nitrogen to freeze. We can go even further, into interstellar space, where the nearest stars will be in light years from us.

At temperatures below 3 degrees Celsius aboveabsolute zero, these barely detectable photons are the only source of heat. Since every place in the Universe is constantly bombarded with these infrared, microwave and radio photons, one would think that 2.725 degrees Kelvin (-270.42 Celsius) is the coldest thing that can be found in nature. To test the temperature colder, you need to wait until the Universe expands even further, stretches the wavelengths of these photons and cools to an even lower temperature. And this will happen, of course, but not soon. At this point, the universe will be twice as old - another 13.8 billion years will pass - and the lowest temperature will hardly exceed at least one degree above absolute zero. However, you can already find a place that is colder than the deepest depths of intergalactic space.

You don’t even have to go far. This is the Boomerang Nebula, located just 5,000 light-years from us, in our own galaxy. In 1980, when it was first observed in Australia, it looked like a bipartite asymmetric nebula, for which it was called the “boomerang”. Subsequent observations have shown that this nebula is actually a pre-planetary nebula, an intermediate stage in the life of dying stars such as the Sun. All such stars evolve into red giants and end their lives in the form of a planetary nebula and a white dwarf, when the outer layers swell and the central core contracts. But between the red giant and the planetary nebula there is a phase of the preplanetary nebula.

All other planetary and preplanetarynebulae are much warmer, but why this happens is easy to explain. Try to take a deep breath, hold your breath for three seconds, and then let the air out. You can do this in two ways by holding your hand at a distance of 15 centimeters from your mouth.

  • You can breathe out with your mouth wide open and feel the warm air gently hit your hand.
  • You can stretch your lips with a tube and blow cold air.
  • In both cases, the air heats up inside yourbody and remains the same temperature before it passes through your lips. But if the mouth is wide open, the air comes out slowly and slightly heats the hand. If it exits through a small hole, the air expands rapidly and cools.

    The outer layers of the star that generated the Boomerang Nebula are in the same conditions:

    • a lot of hot stuff
    • which is quickly thrown away
    • from a tiny point (or rather, two)
    • expands and cools.

    But what is especially interesting is thatThe Boomerang Nebula was predicted even before it was found. Astronomer Rajvendra Sahai calculated that a preplanetary nebula under certain conditions - as described above - can actually reach a lower temperature than all other places in the universe. Sahaya then joined the team in 1995, which made important long-wave observations and determined the temperature of the Boomerang Nebula. Now it is the coldest known place in the universe.