It may sound strange, but the coldest place in the Universe is not anywhere in the vast, cold outer space – it exists here on Earth. Well, it is not actually a natural place you can come across. It is in a laboratory in M.I.T. (Massachusetts Institute of Technology).
In 1995, Wolfgang Ketterle (see notes 1) and his colleagues have cooled a sodium gas to the lowest temperature ever recorded: only half-a-billionth of a degree above absolute zero (see notes 2), which is -273.15°C (-459.67°F), and actually unreachable. They managed to achieve this at Ketterle’s lab, MIT, Cambridge. This accomplishment still holds the record according to Guinness World Records for the lowest temperature. They bested the previous record by a factor of six and is the first time that a gas was cooled below 1 nanokelvin (one-billionth of a degree).
In doing so, Ketterle and his team discovered a new form of matter, the Bose-Einstein condensate, where the particles march in lockstep instead of flitting around independently. The discovery of Bose-Einstein condensates was recognized with the 2001 Nobel Prize in physics, which Ketterle shared with his Boulder colleagues Eric Cornell and Carl Wieman.
But why are the scientists trying to achieve those cool temperatures? According to David E. Pritchard, a pioneer in atom optics and atom interferometry and co-leader of the MIT group, “Ultra-low temperature gases could lead to vast improvements in precision measurements by allowing better atomic clocks and sensors for gravity and rotation”.
The researchers also expect new phenomena to occur at such low temperatures involving, for example, how cold atoms interact with surfaces and how atoms move when they are confined to a narrow channel or layer. These gases form a remarkable state of matter called a quantum fluid, so studying their properties also provides new insights into the basic physics of matter.
At such low temperatures, atoms cannot be kept in physical containers, because they would stick to the walls. Furthermore, no known container can be cooled to such temperatures. Therefore, the atoms are surrounded by magnets, which keep the gaseous cloud confined. “In an ordinary container, particles bounce off the walls. In our container, atoms are repelled by magnetic fields,” explained physics graduate student Aaron Leanhardt.
For reaching the record-low temperatures, the MIT researchers invented a novel way of confining atoms, which they call a “gravito-magnetic trap.” As the name indicates, the magnetic fields act together with gravitational forces to keep the atoms trapped.
The coldest place in the Universe
During their experiment, the German physicist Wolfgang Ketterle and his colleagues managed to reach only half-a-billionth of a degree above absolute zero, which is -273.15°C (-459.67°F), so someplace in their laboratory at the MIT, Cambridge, was practically the coldest place in the Universe.
For comparison, the coldest temperatures recorded are:
- On Earth, -89.2°C (-128°F)
- On Moon, -247°C (-413°F)
- On Mars, -125°C (-195°F)
- In the solar system (Uranus‘ atmosphere), -224°C (-371°F)
Here is the documentary on the Bose-Einstein Condensate work done in Wolfgang Ketterle’s lab, titled “The Coldest Place in the Universe”. By Stephen Craft, Lauren Maurer, and Fangfei Shen. Production of the Graduation Program in Science Writing, MIT.
The “true” Coldest Place in the Universe
According to the Guinness Book of World Records, besides laboratory-created temperatures, “the coldest place in the universe is in the Boomerang Nebula, a cloud of dust and gases 5,000 light-years from Earth. It has a temperature of -272°C (-457.6°F). It is formed by the rapid expansion of gas and dust flowing away from its central aging star. This cold region of the nebula was discovered in 1995 by astronomers using data obtained by the 49 ft wide Swedish-European Space Observatory-Submillimeter radio telescope in La Silla, Chile. In the area’s coldest spots, the gases are believed to be expanding at 370,000 mph (595,457 km/h or 165,404.8 meters per second). Colder temperatures have been achieved in laboratories on Earth.”
The Boomerang Nebula is a young planetary nebula and the coldest object found in the Universe so far. The NASA/ESA Hubble Space Telescope image is yet another example of how Hubble’s sharp eye reveals surprising details in celestial objects.
This NASA/ESA Hubble Space Telescope image above shows a young planetary nebula known (rather curiously) as the Boomerang Nebula. It is in the constellation of Centaurus, 5000 light-years from Earth. Planetary nebulae form around a bright, central star when it expels gas in the last stages of its life.
The Boomerang Nebula is one of the Universe’s peculiar places. In 1995, using the 15-meter Swedish ESO Submillimeter Telescope in Chile, astronomers Sahai and Nyman revealed that it is the coldest place in the Universe found so far. With a temperature of -272°C, it is only 1 degree warmer than absolute zero (the lowest limit for all temperatures). Even the -270°C background glow from the Big Bang is warmer than this nebula. It is the only object found so far that has a temperature lower than the background radiation.
Australian astronomers Keith Taylor and Mike Scarrott called it the Boomerang Nebula in 1980 after observing it with a large ground-based telescope in Australia. Unable to see the detail that only Hubble can reveal, the astronomers saw merely a slight asymmetry in the nebula’s lobes suggesting a curved shape like a boomerang. Later, high-resolution Hubble images indicate that “the Bow tie Nebula” would perhaps have been a better name.
The Hubble Space Telescope took this image in 1998. It shows faint arcs and ghostly filaments embedded within the diffuse gas of the nebula’s smooth “bow-tie” lobes. The diffuse bow-tie shape of this nebula makes it quite different from other observed planetary nebulae, which normally have lobes that look more like ‘bubbles’ blown in the gas. However, the Boomerang Nebula is so young that it may not have had time to develop these structures. Why planetary nebulae have so many different shapes is still a mystery.
The general bow-tie shape of the Boomerang appears to have been created by a very fierce 500,000 kilometer-per-hour wind blowing ultracold gas away from the dying central star. The star has been losing as much as one-thousandth of a solar mass of material per year for 1500 years. This is 10-100 times more than in other similar objects. The rapid expansion of the nebula has enabled it to become the coldest known region in the Universe.
The image was exposed for 1000 seconds through a green-yellow filter. The light in the image comes from starlight from the central star reflected by dust particles.
- Wolfgang Ketterle (born 21 October 1957) is a German physicist and professor of physics at the Massachusetts Institute of Technology (MIT). His research has focused on experiments that trap and cool atoms to temperatures close to absolute zero, and he led one of the first groups to realize Bose-Einstein condensation in these systems in 1995. For this achievement, as well as early fundamental studies of condensates, he was awarded the Nobel Prize in Physics in 2001, together with Eric Allin Cornell and Carl Wieman.
- Absolute zero is the lower limit of any possible temperature. Nothing can be cooler than it – in fact, it is unreachable. More scientifically, it is the lower limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reaches its minimum value, taken as 0. Absolute zero is the point at which the fundamental particles of nature have minimal vibrational motion, retaining only quantum mechanical, zero-point energy-induced particle motion. It is taken as -273.15°C (-459.67°F), which is determined by extrapolating the ideal gas law. The corresponding Kelvin and Rankine temperature scales set their zero points at absolute zero by definition.