The largest comet from the Oort cloud. This is C / 2014 UN271 (Bernardinelli-Bernstein) , a comet that was heading towards the interior of the solar system, has been recognized as the largest ever seen. Its size, 137 kilometers across, is closer to representing that of a minor planet than that of an ordinary comet.
Last year, reviewing data from a project on dark energy, this huge comet was identified that in less than a decade will approach the Sun at a distance slightly greater than that of Saturn, but initial estimates presented a vague figure of between 100 and 200 kilometers in diameter. Its brightness suggested that it was a large object. Now, a new study gives a more specific precision to this great comet: 137 kilometers in diameter, similar to the distance between the American cities of New York and Philadelphia.
Never seen on kites
With this figure, comet C/2014 UN271 (Bernardinelli-Bernstein) unseats Hale-Bopp from first place, about 70 kilometers wide and which could be seen in the skies of the 20th century for 18 months.
Finding bright comets is a once-in-a-few-years event, but finding a mega-comet bright enough to catch our attention is an even rarer event. Hale-Bopp hurtled down from the outer solar system and gave us one of the most spectacular celestial spectacles in modern history.
It was the astronomers Pedro Bernardinelli and Gary Bernstein from the University of Pennsylvania (USA) who discovered this giant comet after looking in detail at the data from the Dark Energy Survey (DES), hence the name of the comet: for the year in which it was first recorded and by the name of its discoverers.
How have they determined their size?
Scientists used microwave radiation to search for precision not available in visible light. Instead of trying to measure how much of the sky 2014 UN271 took up, they looked at how much heat it emitted and used that to calculate the comet’s surface area. To do this, they used the Atacama Large Milimeter Array (ALMA) located in Chile, studying four wavelengths between 1 and 2 millimeters. Thanks to this they concluded that it must be 137 kilometers wide (with a difference above and below 17 kilometers) to produce the radiation detected by the instruments.
Measuring the width of an object that is more than 3 billion kilometers away is difficult , because comets are icy bodies that evaporate as they approach the heat of the Sun, growing their cometary shell of dust and gas around the solid object. .
This megacomet will reach perihelion (its closest distance from the Sun) in January 2031 . At this time, it will be slightly beyond the orbit of the planet Saturn and we will be able to observe it from the northern hemisphere of the Earth. However, astronomers don’t expect the comet to brighten enough for us to see it on Earth without powerful telescopes.
Referencia: E. Lellouch, R. Moreno, D. Bockelée-Morvan, N. Biver, P. Santos-Sanz . Size and albedo of the largest detected Oort-cloud object: comet C/2014 UN 271 (Bernardinelli-Bernstein) arXiv:2201.13188 [astro-ph.EP]
Accepted for publication in Astronomy and Astrophysics Letters,
Referencia: (National Optical-Infrared Astronomy Research Laboratory) NOIRLAB
