Some stars eventually evolved into white dwarf remnants. This compact dead star has the mass of the sun, but the volume is similar to that of the earth, and the density is quite amazing. However, astronomers have recently found the smallest white dwarf star to date. The mass is 1.35 times that of the sun, but the size is only slightly larger than the moon, just like a monster.
White dwarfs are the final evolutionary state of stars whose mass is usually less than 8 times the mass of the sun. About 97% of the stars in the universe have their final destiny trends. Only massive stars may collapse into neutron stars or black holes after they explode. Our sun is expected to expand into a red giant in 5 billion years, after which the outer layer will fall off to form a planetary nebula, and the inner core will shrink into a compact white dwarf.
Most of the known white dwarfs have masses in the range of 0.5 to 0.7 solar masses, and their radii are mostly in the range of 0.008 to 0.02 solar radius. That is to say, these white dwarfs have the same mass as the sun, but their internal organs are all squeezed within the same size as the earth. As a result, the average density of white dwarfs is about one million times that of the sun. It is one of the most densely known celestial bodies. Only the density of neutron stars, black holes and theoretical quark stars can surpass that of white dwarfs.
Several special cases of white dwarf stars have also been discovered in the past. The lowest estimated mass is 0.17 times the mass of the sun and the highest is 1.33 times. However, scientists now use the Zwicky Transient Facility (ZTF) to find a mass 1.35 times the sun, but A super-compressed white dwarf star with a volume only slightly larger than the moon, named ZTF J1901+1458. Its radius is about 2,100 kilometers. It is very close to the moon’s radius of about 1,700 kilometers. In contrast, most white dwarfs are close to the Earth in size and have a radius of about 6,300 kilometers.
According to analysis, ZTF J1901+1458 has an extreme magnetic field that is nearly 1 billion times stronger than that of the sun, and it rotates once every 7 minutes at a crazy speed (the other most active white dwarf known is EPIC 228939929, which rotates every 5.3 minutes). ring).
The team said that this white dwarf star is likely to be formed by two white dwarfs orbiting each other and finally merging, so as to give it the characteristics of small size, strong magnetic field and accelerated rotation. ZTF J1901+1458 may come from a binary star system composed of two white dwarfs. Over time, the two eventually merged into one. It was originally expected that this situation would explode to form a Type Ia supernova, but the mass of the system was just enough to merge into a white dwarf star.
In the end, this white dwarf star with an amazing contrast in mass and size may evolve into a neutron star. If it does so, we may find another hypothesis for the formation of neutron stars, and even indicate that some neutron stars may be white dwarfs.
The new paper was published in the journal Nature.
(Source of the first image: Keck Observatory)
