To the naked eye, the night sky has more than 9.000 points of light, but this observable part is only a small corner of the universe.
Simulated flash of light erupting from the star Proxima Centauri. Image: NRAO/S. Dagnello
The closest visible (visible) star system is Alpha Centauri, about 4,25 light years from Earth. The closest star in this triple star system is Proxima Centauri, but because it is a red dwarf, it is too faint to observe without a telescope.
The farthest star the naked eye can see is V762 Cas, a variable star 16.000 light years from Earth. Although it can be 100.000 times brighter than the Sun, its distance is so far that it is only just enough to be observed with human night vision under ideal conditions.
Every star that humans see with the naked eye has a mass much greater than the Sun. Stars the size of the Sun or smaller are not bright enough to overcome the light-year distance between them and Earth, thus becoming invisible.
V762 Cas is the most distant star visible to the naked eye, but not the most distant object observable without a telescope. This title belongs to the Andromeda galaxy. Containing more than a trillion stars, to the human eye this galaxy appears as a blur as large as an outstretched fist. When looking at Andromeda, the observer is receiving light transmitted 2,5 million years ago.
Additionally, there are some flashes and explosions that temporarily increase their brightness to incredible levels, making them briefly visible even at extremely great distances. For example, in 2008, the GRB 080319B gamma-ray burst could be seen with the naked eye for about 30 seconds, even though it was more than 7,5 billion light years away. This means that when the light from the explosion began to propagate, the solar system had not even formed yet.
A distant galactic region photographed by the James Webb space telescope. Image: NASA/ESA/CSA/STScI
Telescopes allow people to observe fainter objects because they collect more light, and to observe more distant objects because they help magnify the image. However, even with the most advanced ground and space telescopes and the most extensive surveys, scientists have only mapped less than 3% of the stars in the Milky Way and have not yet 1% of galaxies in the observable universe.
To observe more distant objects, experts take advantage of a unique natural phenomenon: When light from a distant star or galaxy passes through a giant cluster of objects, the cluster's gravitational pull can can magnify images, sometimes more than 10.000 times.
This phenomenon is called gravitational lensing. Thanks to this, astronomers were able to detect the most distant single star ever recorded, Earendel. Earendel appeared only about 900 million years after the Big Bang, belonging to the first generation of stars in the universe. Although light from Earendel takes 12,9 years to reach Earth, this star is currently more than 28 billion light years away from Earth because the universe has expanded more rapidly since the Big Bang.
Also with gravitational lensing, astronomers used the James Webb space telescope to accurately measure the distance to JADES-GS-z13-0, the most distant galaxy ever recorded. JADES-GS-z13-0 is currently more than 33,6 billion light years from Earth and formed when the universe was only 400 million years old. Experts say that people can still see more distant cosmic objects in the future.
Thu Thao (Follow Space)
