How Do Scientists ‘Weigh’ Stars?
The stars are huge balls of hot gas located several thousand kilometers away, but when viewed from Earth, they appear as small points of visible light in the night sky. In a new study, astronomers have accurately measured the mass of a “white dwarf” near a star that has reached the end of its life cycle. But exactly how can this be done? How do scientists “heavy” the mass of a gaseous sphere a few light years?
“The only way in which astronomers measure the masses of stars, planets and galaxies through their gravitational influence on others,” said Terry Oswalt, a professor of physical engineering at Embry-Riddle Aeronautical University who wrote a Comment on the recent measurement of white dwarfs in the journal Science.
In other words, if a satellite is in orbit around Jupiter, it is possible to estimate the mass of Jupiter by measuring the effects of gravity on the planet in the orbit of satellites. [The 18 Greatest Unresolved Mysteries in Physics]
Such estimates can be made with stars as well. Sensitive instruments such as NASA’s Kepler Space Telescope can detect planets orbiting stars through the Milky Way by measuring small variations in the velocity of stars as “back” planets in their orbits, Oswalt explained. These measures can also provide researchers with information about the masses of stars.
When two stars around each other, as is the case with binary stars, astronomers can measure their motion using the Doppler effect, based on the same principle as a police radar pistol, according to Oswalt. However, this technique requires that objects are observable.
“There are several indirect ways to estimate the mass of a star in its [light] spectrum, but they depend on a detailed model of the atmosphere, you never know for sure,” Oswalt said.
The new technique, described in a study published online June 7 in the journal Science, allows astronomers to estimate that stars of mass and other celestial objects, including intrinsically dark white dwarfs, black holes and furious planets (the worlds Which were dumped from their solar system), which are difficult to observe with telescopes.
The study, led by astronomers at the Space Telescope Science Institute in Baltimore, showed how the researchers measured a nearby white dwarf called Stein 2051 B. The technique is based on the influence of gravity on light.
“In his famous equation E = mc ^ 2, Albert Einstein postulated that energy and mass are the same thing,” Oswalt said. “Light is a bit of energy and equivalent mass even stronger, but it is also affected by gravity.” [8 ways to see Einstein’s theory of relativity in real life]
Einstein also predicted that a beam of light from a distant star through an object is slightly bent due to the gravitational pull of this object. For the effect that was observed, the two objects must enter a nearly perfect alignment, which according to Oswalt, is quite rare.
“As the light of the background star passes through the white dwarf, the direction of a straight line is curved, and this means that the light we will see seems to come from a direction different from that of the true star, Which makes dwarf motions slowly through the background stars, as if the background star made a small loop in the sky, “Oswalt said.
“The basic idea is that the apparent deviation of the background star’s position is directly related to the mass and gravity of the white dwarf – and how the two got to align exactly,” Oswalt said.
The effect, called gravitational microlentisseur was previously observed on a much larger scale during total eclipses or participation of objects more distant Stein 2051 B. In these distant objects, gravity acts as a lens that bends light from stars and, Therefore, illuminate the source of light, according to Oswalt. In the case of very distant galaxies we can see an effect known as the Einstein ring – a distortion of light due to gravity.