NASA has announced that it has isolated the mass and location of what could be a “wandering” black hole using the Hubble Space Telescope. This is the first time in the space agency’s history it has been able to achieve this, despite there being over 100 million black holes populating our galaxy.
Up until now, black holes have largely been considered
theoretical, with measurements being taken on their influence upon other
interstellar bodies, rather than the holes themselves. Measuring the effect it
has on the stars around it is how NASA has identified the presence of the black
hole in the past.
But after six years of using the Hubble to observe the
Carina-Sagittarius spiral arm of our galaxy, NASA was able to detect the black
hole travelling through the arm about 5,000 light-years away. Taking a wandering
path through the galaxy is unique for this black hole, as scientists believe
that most either occupy the core of a galaxy or are paired with a binary system
nearby, which is how they can be observed, through its interaction.
But this wandering hole is a solitary traveler in our
galaxy, leading scientists to conclude that when the black hole was formed
millions of years ago, it received a “kick” from the supernova that created it,
which provided the momentum to send it on a journey throughout the galaxy.
“Black holes roaming our galaxy are born from rare,
monstrous stars (less than one-thousandth of the galaxy’s stellar population)
that are at least 20 times more massive than our Sun,” says the NASA statement
announcing the find.
“These stars explode as a supernova, and the remnant
core is crushed by gravity into a black hole. Because the self-detonation is
not perfectly symmetrical, the black hole may get a kick, and go careening
through our galaxy like a blasted cannonball.”
Hubble can’t actually take a picture of the black
hole, since it sucks in all light, rather than reflect it. But as the black
hole warps space through its interaction, the light coming from surrounding
stars is bent and is actually amplified as the black hole travels in front of
it, giving astronomers the ability to observe it. Additionally, astronomers are
able to rule out the effects of neighboring stars since there is no color shift
when the rotating starts move into alignment.
Two teams observed the black hole, using data from
Hubble to ascertain the wandering Black hole’s position, both coming to
slightly different conclusions as to size, but agreeing that the hole is
present and largely compact.
Four Times Bigger Than Our Sun
The data was collected using a technique known as
“Astrometric microlensing,” which can be used to detect objects that range from
the mass of a planet to the mass of a star, regardless of the light they emit.
The technique, which was postulated by Albert Einstein in his seminal 1916
paper on general relativity, was developed by astronomers a few years later, to
measure a background star being offset by two arc seconds, thereby validating
Einstein’s theories.
The Hubble observed the nearby light as it was
amplified and warped over a 270-day period, and the teams took another six
years to process the data and come to the conclusion that it may be a black
hole travelling through our galaxy.
But even though the teams believe that phenomenon is a
black hole, they also admit it could be the effects of a nearby neutron star.
The estimated mass of the invisible compact object is measured to be between
1.6 and 4.4 times that of the Sun. At the high end of this range, the object
would be a black hole; at the low end, it would be a neutron star.
“As much as we would like to say it is definitively a
black hole, we must report all allowed solutions. This includes both lower-mass
black holes and possibly even a neutron star,” said Jessica Lu of the Berkeley
team.
“Whatever it is, the object is the first dark stellar
remnant discovered wandering through the galaxy, unaccompanied by another star”
Lam added.
The team estimates that the object has a mass of over
seven solar masses and is traveling through the Milky Way galaxy at over
100,000 miles an hour.
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