At just one degree above absolute zero, the coldest place in the Milky Way isn't a frozen, empty void. It's a dying star violently expelling gas at 164 kilometers per second.
Known as the Boomerang Nebula, this system is located about 5,000 light-years from Earth in the constellation Centaurus. At just 1 Kelvin (−272.15 °C or −457.87 °F), it is colder than the cosmic microwave background radiation (2.7 Kelvin), the faint afterglow of the Big Bang that establishes a baseline temperature for empty space. The Boomerang Nebula is the only object ever discovered that is naturally colder than the background radiation of the universe itself.
This extreme cold is not caused by an absence of energy, but by rapid thermodynamic expansion. The Boomerang Nebula is in a brief transitional phase known as a pre-planetary nebula. Its central dying star is shedding its outer layers into space, losing mass about 100 times faster than similar objects.
When a gas expands rapidly without any heat being added, its temperature drops—a phenomenon known as adiabatic cooling. This is the exact same principle that causes a can of compressed air to turn cold in your hand when you hold the trigger. The dying star is ejecting gas so fast and expanding it so quickly that the nebula acts as a cosmic-scale refrigerator, dropping the temperature of the surrounding gas down to near absolute zero.
When astronomers first observed the object with ground-based telescopes in 1980, its slightly curved appearance led them to name it the Boomerang Nebula. However, when the Hubble Space Telescope later captured the system in high resolution, the imagery revealed that the visible gas actually forms a highly symmetric bow-tie shape. Later observations with the ALMA radio telescope demonstrated that even this visual is a partial illusion; a dense disc of dust blocks visible light around the star's equator, allowing illumination to leak out only through the two opposed lobes.