No one knows how many black holes there are in the universe
Black holes do not emit any light of their own making them impossible to see directly with telescopes.
The only way we can detect black holes is by looking at the effects they have on things we can see.
When a black hole resides near another star,
we can see the elongated shape of the star as material is pulled away
by its incredible gravitational pull
We can also see the high energy radiation that accelerates away
from the spin axis of the black hole generated by infalling material
This is x-ray and gamma radiation that, if directed towards Earth, are among the brightest objects in the universe
A new technique that’s only recently been possible with our latest telescopes
is that of gravitational lensing
We can see background stars flash brighter as their light
is magnified by the gravity of a black hole
creating a lens that bends the light traveling towards us
making a momentary flash of light that we can detect
We’ve theorized about black holes for centuries
and they were a prediction of Einstein’s theories of relativity
but it was only recently that we’ve managed to directly image
the region around a black hole
In 2019, the Event Horizon Telescope collaboration took this image
of the black hole at the center of the galaxy called M87.
Called M87 star, this is a direct image of the area around a
supermassive black hole some six and a half billion solar masses
What’s shown here is the clear delineation that marks the event horizon
A boundary that once crossed, allows no light - or nothing else for that matter - to escape
A second image was released in 2021 of the black hole
at the center of our galaxy - called Sagittarius A star - a 4 million
solar mass black hole devouring material and emitting radiation
The images from the Event Horizon team are the first direct images
and proof that black holes actually exist
So from all of our theories and observations, the conclusions
are that there is probably a supermassive black hole
with masses millions of times that of our Sun
embedded in the centers of every galaxy in the universe
We see them as quasars from all corners of creation
But what about the smaller ones?
What about the black holes the sizes of stars, so-called stellar-mass black holes?
These are created when stars like Betelguese die
they explode in supernovae creating an astounding nebula and
leaving behind either a neutron star or a black hole.
How many of them are there?
Since we can only see a black hole by observing its effect on its surroundings
we can’t know this for sure
Some black holes are lurking in the space between the stars
silently floating in interstellar space
We would never know they are there until
they get close to something we can see
With that scary prospect in mind, it is a reasonable question to ask
what’s the closest known black hole to us?
The answer is surprisingly elusive
Astronomers from the Event Horizon Telescope collaboration
tell us that the closest known black hole is V616 Monocerotis
an 11 solar mass black hole some 3,000 light years away
It orbits a one half solar mass k-type star every 8 hours
The next one farther out at double the distance, 6000 light years
is the 15 solar mass black hole Cygnus X-1
But there is another tantalizing possibility.
A black hole much much closer than v616 Monocerotis and Cygnus X-1
There is evidence of a ten solar mass black hole surrounding the double star system V Puppis
This system consists of two B-class stars orbiting extremely close to each other some 1165 light years away
These stars are so close together that they orbit each other once every 1.5 days
and as they do so, they block each other with respect to Earth’s line of sight
These sorts of binary systems are called eclipsing binaries
As they orbit each other, blocking out the light from their companion
our telescopes on Earth measure a light curve that shows a
dipping and brightening as each star eclipses the other
But astronomers noticed something else
The period of the light curve was not what would be expected if these two stars were alone
Something else was noticed
creating a strange periodicity in the light curve that indicated there was something else out there
Something with a gravitational pull equal to ten solar masses
Upon searching, nothing in any visible, infrared, ultraviolet,
x-ray, gamma ray, or radio wavelengths were seen
Whatever was there, was invisible
Whatever was there, was also too massive to be a planet or several planets
Astronomers suggest that a ten-solar mass black hole is circling both stars
about 10 astronomical units away, tugging on them,
creating the strange period in their light curves
If this is true, then V Puppis is home to the closest known black hole
and because these stars are bright, about as bright as the star Vega in our night sky
V* V Puppis is also the first naked-eye black hole
The constellation Puppis is visible just below Canis Major in the Winter sky in the northern hemisphere
Looking for bright blips in the sky is probably our best bet
for finding more silent and dark black holes in our galaxy
This technique, called gravitational microlensing
is utilized in many sky surveys like the Dark Energy Survey
and the upcoming Large Synoptic Sky Survey using the Vera Rubin Telescope
Seeing first light in 2023, this telescope will look at the entire sky
several times each week allowing astronomers to scour the resulting data
and look for hundreds, perhaps thousands of tiny blips of light
betraying the locations of these celestial ninjas