Scientists have long been interested in the question: how cold it is in space. As a rule, the temperature there is not lower than the temperature of the relic radiation, which permeates the entire Universe. However, in places where stars die, temperatures can drop much lower. Scientists managed to find such a place in the planetary Boomerang nebula.
The average temperature on Earth, a planet that is more than 149 million kilometers from the Sun, is kept within 300 K. It should be noted that the planet is still heated by the hot core, and in addition, in the absence of the atmosphere, the temperature indicators would be another 50 K less. The farther an object is from the nearest star, the colder it is. For example, on Pluto, the average temperature is only 44 K. At such rates, even nitrogen freezes, which means that there would be practically nothing left of the earth's atmosphere, because it contains 80 percent nitrogen. Outside the solar system, in interstellar space, it is much colder.
Molecular clouds float around the galaxy, the substance in which has a temperature of about 10-20 K, which is close to absolute zero. There are no lower temperatures in the galaxy anymore, since the rest of its parts are warmed to one degree or another by stellar radiation.
However, in intergalactic space, the temperature is even lower than in a molecular cloud, which is far from radiation sources. The Galaxies are separated by millions of light-years of void, and the only radiation reaching all corners of space is microwave background radiation, which is left from the Big Bang. Due to the waves of the relict radiation, the temperature in intergalactic space does not drop below 2.73 K. At first glance, it may seem that it simply cannot be colder, but in reality this is far from the case.
More precisely, it could theoretically be colder. In order for the temperature indicators of intergalactic space to drop below 2.73 K, it is necessary to wait for the Universe to expand slightly. This expansion is already taking place - the universe is expanding at a speed of about 770 kilometers per second over 3.26 million light years. Currently, the age of the Universe reaches 13.78 billion years, and when it becomes twice as large, the relic radiation will be able to keep the temperature only one degree above absolute zero.
Temperature map of the preplanetary Boomerang nebula
And the most unexpected news from scientists: the coldest place in the Universe can be found already at this moment, and not very far from the Earth - in the Boomerang nebula, located only 5 thousand light years from our planet.
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In the center of this nebula is a dying star, which was in the past like the Sun, a yellow dwarf. Like the rest of the stars of the same spectral class, it became a red giant and ended up in a system that arose from a white dwarf and a preplanetary nebula that arose around it.
The planetary nebula is usually called the remnants of the peripheral areas of the red giant, ejected by the star during the period when its center shrank to the size of a white dwarf. But, before becoming a planetary nebula, the red dwarf becomes a preplanetary nebula for a while. In the event that all the necessary conditions arise in it, the temperature indicators in the nebula can fall below the lowest temperatures in the Universe. Indian astronomer Ravendra Sahai came to similar conclusions, and, much earlier than his team created a temperature map of the Boomerang Nebula and made sure that it is really very cold there.
The Boomerang Nebula is the coldest place in the universe
Photo: ESA / NASA
A preplanetary nebula arises when the temperature in the star's core rises, but at the same time the peripheral matter is just beginning to separate. This process occurs with several ejections of plasma streams that begin in the outer layer of stellar matter. According to cosmic standards, these streams exist for a very short time - only a few thousand years. Provided that the plasma in the stream moves rapidly (and in the Boomerang nebula this is exactly the case), then the loss of matter by the star occurs at a high speed. It is due to this tremendous speed in the nebula that those regions arise in which the temperature index does not exceed 0.5 K, which is significantly lower than the temperature in any other place in the universe.
And all because the thermal energy of the molecules is converted into kinetic energy of motion, due to which the air cools down.