The newly discovered white dwarf is about 100 million years old

The newly discovered white dwarf, the smallest and heaviest known white dwarf discovered, designated ZTF J190132.9 + 145808.7 (ZTF J1901 + 1458), has a mass of 1.35 solar masses and a radius of 2,140 km (1,330 miles) and only slightly larger than the radius of the Moon.

Newly discovered white dwarf

This illustration shows the newly discovered white dwarf ZTF J190132.9 + 145808.7 and the Moon. Image credit: Giuseppe Paris. ZTF J1901 + 1458 is located about 130 light years distant in the constellation Aquila. The white dwarf is about 100 million years old and has a magnetic field about a billion times greater than that of our Sun.

It has a rotation period of 6.94 minutes, unusually short for a white dwarf, since the rotation periods of white dwarfs are usually more than hours. “ZTF J1901 + 1458 is massive, it packs more mass than our Sun into a body the size of our Moon,” Dr. Ilaria Caiazzo said.

White dwarf

It may seem counterintuitive, but the smaller white dwarfs are more massive. This is due to the fact that white dwarfs lack the nuclear combustion that normal stars maintain against their own gravity, and their size is controlled by quantum mechanics. ZTF J1901 + 1458 was discovered by the Zwicky Transient Facility (ZTF), which operates at Caltech’s Palomar Observatory.

“Until now no one has been able to systematically detect short-lived astronomical events on such a scale. The results of these efforts are surprising,” said Dr. Kevin, a postdoctoral researcher in Caltech’s Department of Physics, Mathematics and Astronomy. The astronomers then imaged ZTF J1901 + 1458 using data from various space and ground-based telescopes.

The strength of the magnetic field, along with the object’s 7-minute rotation speed, indicated that it was the result of two small white dwarfs colliding into one. Many stars orbit each other in pairs. They age together, and if they both have less than 8 solar masses, they will both evolve into white dwarfs, the researchers said.

discovered white dwarf

The new discovery provides an example of what can happen after this stage. The pair of newly discovered white dwarf, which orbit each other, lose energy in the form of gravitational waves and eventually merge. If dead stars are big enough, they explode in a Type Ia supernova. But if they are below a certain mass threshold, they clump together into a new white dwarf that is heavier than any parent star.

This fusion process increases the magnetic field of that star and accelerates its rotation compared to the mother. ZTF J1901 + 1458 took another development path; Their ancestors merged and produced a white dwarf 1.35 times the mass of our Sun. The discovery is reported in an article in the journal Nature.

The smallest and densest white dwarf ever discovered packs the mass of the Sun into a stellar corpse the size of the Moon. The white dwarf ZTF J1901 + 1458 is depicted on the Moon in this artist’s rendering; In fact, the white dwarf is located at a distance of 130 light years from Earth, in the constellation Aquila, Aquila.


The white dwarf ZTF J1901 + 1458 is depicted on the Moon in this artist’s rendering; In fact, the white dwarf is located at a distance of 130 light years from Earth, in the constellation Aquila, Aquila. (Image credit: Giuseppe Paris). Astronomers may have discovered the smallest and heaviest white dwarf star ever observed, a smoking ember the size of our moon but 450,000 times more massive than Earth, according to a new study.

White dwarfs are usually the size of Earth and have cold, faint cores of dead stars that remain after medium-sized stars have used up their fuel and discarded their outer layers. Our Sun will one day become a white dwarf, as will 97% of all stars. Although the Sun is alone in space without a stellar companion, many stars orbit each other in pairs. If these binary stars are less than eight times the mass of the Sun, they will both become white dwarfs over time.

The newly found white dwarf, designated ZTF J1901 + 1458, is located about 130 light years from Earth and may be an example of what can happen when pairs of white dwarfs merge. If white dwarfs were more massive, they would explode in a powerful thermonuclear explosion, known as a Type Ia supernova. However, if their combined mass fell below a certain threshold, they could form a new white dwarf larger than its parent, which scientists believe happened in the case of ZTF J1901 + 1458.

Smallest white dwarf in history

“Our discovery is the largest and smallest white dwarf in history,” lead study author Ilaria Caiazzo, an astrophysicist at the California Institute of Technology in Pasadena, told The discovery was made using the Zwicky Transitional Facility at the Palomar Observatory in California, which scans the entire northern sky every other night, looking for cosmic objects that similarly flicker, explode, move or change in brightness. Co-author Kevin Burge, an astrophysicist at the California Institute of Technology in Pasadena, first observed new white dwarfs based on their large mass and fast spin.

The researchers used several telescopes to help analyze the dead star, which is about 100 million years old or younger. These include the Hale Telescope at Palomar, the W.M. The Keck Observatory’s Keck I telescope, the European Gaia Space Observatory, the Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) at the University of Hawaii, and NASA’s Swift Neil Gehrels Observatory.

The scientists found that the white dwarf was about 2,670 miles (4,300 kilometers) across, making it slightly larger than the moon, which is about 2,158 miles (3,474 km) in diameter. The small size of ZTF J1901 + 1458 makes it the smallest known white dwarf, eliminating previous record holders RE J0317-853 and WD 1832 + 089, each of which is approximately 3,100 miles (5,000 km) in diameter.

Smallest known white dwarf

Furthermore, the newly detected white dwarf is about 1.35 times the mass of our Sun, which could make it the most massive white dwarf ever discovered. Caiazzo said it may be a bit of a contradiction that the most massive known white dwarf is also the smallest white dwarf. This is because gravity and other factors make white dwarfs more massive the smaller they are.

This white dwarf is just below the mass at which one would expect a white dwarf to explode. “It’s really on the border,” Caiazzo said. If it were a bit heavier, it would have exploded. The white dwarf spins very rapidly, completing one revolution every seven minutes. When their parent stars spiraled together to merge, ZTF J1901 + 1458 inherited their combined spin, the researchers said.

normal white dwarfs

The fastest orbiting white dwarf, called EPIC 228939929, rotates every 5.3 minutes. The accelerated spin speed of the white dwarf also helps give it a very powerful magnetic field, one billion times stronger than Earth’s. All these characteristics, its mass, spin and high magnetic field, suggest that this white dwarf was not born in the same way as normal white dwarfs, Caiazzo said.

Because this white dwarf is so massive, it is possible for it to collapse further, as the incredible pressure within its nucleus forces electrons to fuse with protons in atomic nuclei to form neutrons. “It could be even smaller than the Moon,” Caiazzo said, probably shrinking smaller, about 1,240 to 1,865 miles (2,000 to 3,000 km) wide.

If this contraction occurs, perhaps 100 million to 200 million years from now, the white dwarf could destabilize and explode as a Type Ia thermonuclear supernova, Caiazzo said. Another possibility is that if a large number of electrons are captured, the white dwarf could form a neutron-rich dead star known as a neutron star.

Smallest white dwarf

“A neutron star is an extremely dense object that has the mass of the Sun, but the size of a city, so it is even more extreme than this white dwarf,” Caiazzo said. If a white dwarf collapses to form a neutron star, the merging atoms within its core will release enormous amounts of heat, possibly within a few hours or days. “All the white dwarf will burn very quickly,” Caiazzo said.

Neutron stars are typically considered supernovae when they explode stars much larger than our Sun, Caiazzo explained. If giant white dwarfs can also become neutron stars, then a significant number of neutron stars can be produced in this way. However, if the core of a white dwarf solidifies into a crystalline solid faster than it shrinks, it is unlikely to collapse.

white dwarf mergers in the Milky Way

We do not know if such a collapse can occur, and if it does, what consequences, “Caiazzo said.” But if white dwarfs can form neutron stars, then this is a very common form of neutron star formation. . In the future, scientists hope to find more white dwarfs of this type and use the Zwicky transient facility to analyze white dwarfs as a whole.

There are too many questions to address, such as what is the rate of white dwarf mergers in the Milky Way, and is this enough to explain the number of supernovae in Ia? Caiazzo said in a statement. “How do these powerful events generate a magnetic field and why is there so much variation in the intensity of the magnetic field among white dwarfs? Detecting a large population of merger-born white dwarfs can help us answer all these questions.” Scientists detail his findings. online June 30 in the journal Nature.

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