Thursday, astronomers announcement that they used NASA’s Hubble Space Telescope to directly measure the mass of a star’s corpse for the first time. But most importantly, they did it by harnessing a mind-bending cosmic effect called gravitational microlensing, predicted by Albert Einstein’s theory of general relativity over a century ago.
This Hubble achievement marks the first time such an effect has been used to measure a single isolated star other than our own sun.
I’ll get to the subject of microlensing in a moment, but here are some quick statistics on historical white dwarf measurements.
First of all, it is called LAWD 37. Insert “oh lawd he come‘” Cat meme. Sorry.
Second, this lone stellar body, which is the superhot, surviving core of a sun-like scorched star, appears to be 56% of the mass of our sun, according to Hubble observations. This is a real relief because this figure, according to the research team, agrees with previous theoretical predictions about LAWD 37 and solidifies many of our current theories on the structure and composition of white dwarfs. And understanding white dwarfs is crucial to our understanding of the universe.
“White dwarfs give us clues about the evolution of stars – one day our own star will eventually become a white dwarf,” said Peter McGill, postdoctoral researcher at UC Santa Cruz and lead author of a study on measurements published in Monthly Notices of the Royal. Astronomical Society, said in a press release.
Because this particular white dwarf is so close to us at about 15 light-years away, McGill says, we have a lot of data about it. “But the missing piece of the puzzle was a measure of its mass.” Luckily, however, we now have that piece too.
This is where Einstein’s theory comes in.
What is Gravitational Microlensing?
Since its genesis in the early 1900s, scientists have remained absolutely captivated by Albert Einstein’s astonishing theory of general relativity – an idea that rests on the strange premise that our cosmic expanse is physically woven with tangible threads of space and time.
Not only has general relativity yet to be disproven, despite decades of experts trying to find a way out, but it also explains some of the weirdest things happening in our universe. Things like black hole collisions that send gravitational waves reverberating through spaceand time flows differently in Earth’s orbit than on its soil.
But one of astronomers’ favorite general relativity effects is that light in the distant universe appears to bend, twist and warp as it travels through the presence of extreme gravity pools generated by massive compact objects such as than clusters of galaxies. This is called gravitational lensing – and on a smaller scale, gravitational microlensing.
Gravitational lensing is an important phenomenon for astronomy because anything that emits these distorted beams of light (a star, for example) can appear magnified to an observer who would otherwise be unable to see it. On the other hand, you can infer information about anything that causes light beams to distort by working backwards.
And that is precisely what McGill and his fellow researchers have benefited from.
This artist’s illustration shows how the gravity of a white dwarf star warps space and deflects light from a distant star behind it.
NASA, ESA, Ann Field
To start, astronomers used the European Space Agency’s Gaia satellite – a device currently trying to create a wonderfully detailed map of the Milky Way galaxy – to determine where Hubble should be looking for LAWD 37 during a probable gravitational microlensing event.
Next, they observed light from a background star pass behind LAWD 37, its light distorted by the Hubble point of interest.
The team finally understood the vital parameters of how the background star light changed in the presence of LAWD 37 and, through the art of deduction, learned what kind of star mass would produce such changes. Here is.
This graph shows how the microlens was used to measure the mass of a white dwarf. The inset shows how the dwarf passed in front of a background star in 2019. The wavy blue line traces the dwarf’s apparent movement across the sky as seen from Earth.
NASA, ESA, Peter McGill, Kailash Sahu, Joseph DePasquale
“The accuracy of LAWD 37’s mass measurement allows us to test the mass-radius relationship for white dwarfs,” McGill said. “That means testing the properties of matter under the extreme conditions inside this dead star.”
In 1919, just a few years after Einstein published a paper describing the theory of general relativity, two British astronomers used this type of lensing effect to similarly observe the mass of the sun during an eclipse. solar. It was a big moment because it was considered the very first experimental project proof of relativityaccording to NASA – but it was unclear at the time if anyone would again be capable of “gravitational lensing”.
“These events are rare and the effects are minimal,” McGill said. “For example, the size of our measured effect is like measuring the length of a car on the moon as seen from Earth, and is 625 times smaller than the effect measured during the 1919 solar eclipse.”
Going forward, the team wants to continue using Gaia to predict when possible gravitational microlensing events might help them get as many star mass measurements as possible. In fact, Hubble principal investigator and study co-author Kailash Sahu is already working on observing another white dwarf, named LAWD 66, with NASA’s James Webb Space Telescope.
Given how powerful the JWST is, I for one can’t wait to see the next level of gravitational microlensing unfold.
