There are few scientific concepts that are as famous as Albert Einstein's theory of general relativity, but even the iconic theory isn't set in stone.
Einstein's theory of general relativity states that gravity is the result of mass warping space and time with greater mass creating a greater gravitational pull. A century after the famous physicist came up with the theory, it's still proving to be right.
UCLA professor of physics and astronomy Andrea Ghez says that while the theory of general relativity is starting to fray at the edges, it still holds up after her team's comprehensive new analysis of the supermassive black hole at the center of the galaxy.
Gravitational Redshift Proves Einstein Was Right
The general relativity theory predicts an effect known as gravitational redshift, which refers to gravity affecting light. According to this effect, light traveling through the extreme gravitational field of a black hole should lose some energy and slow down, causing the light to appear toward the red end of the spectrum.
Gravitational redshift is at the center of a new study published in the journal Science, where researchers observed a cluster of stars orbiting the supermassive black hole Sagittarius A* found in the core of the Milky Way. The black hole is 4 million times the mass of the sun and is about 26 light-years away from Earth.
For the study, the team specifically kept an eye on the star S0-2 as it made a complete orbit in three dimensions around the black hole. Its full oval-shaped orbit takes about 16 years.
When S0-2 made its closest approach to SgrA* in 2018, Ghez and the other researchers found that the star slows down by about 125 miles per second. These numbers are consistent with Einstein's equations, which indicates that gravity is closer to Einstein's theory of general relativity than the Newtonian model that doesn't account for gravitational redshift.
"This kind of experiment is the first direct test of how gravity works near a supermassive black hole," Ghez told National Geographic, pointing out that gravity is significant not just in human understanding of the universe but also in regular everyday life.
Will Einstein's Theory Always Stand?
As National Geographic noted, astronomers are looking for evidence that show general relativity don't work in extreme gravitational situations, which would give them greater insights into new types of physics that may be crucial to understanding the larger scale of the universe.
While the recent observations and analysis agree with Einstein's theory of general relativity, the authors acknowledge that the 100-year-old theory is starting to show its vulnerability.
"It cannot fully explain gravity inside a black hole, and at some point we will need to move beyond Einstein's theory to a more comprehensive theory of gravity that explains what a black hole is," Ghez pointed out.
For now, Einstein reigns supreme.
