Black Holes, The Enigmas of the Universe
- Amrutha Tummala
- Jun 21, 2020
- 6 min read
Updated: Jun 26, 2020
Of all the constellations in the night sky, Orion the Hunter is perhaps the most well known. The blue supergiant Rigel is the brightest star in the constellation, located in the lower right corner of Orion. Rigel--and all of the other luminous stars dotting our beautiful night sky--may shine brightly now, but all things must eventually come to an end. Yet for supergiants like Rigel, one could argue that a star never truly dies. Instead, its death marks the violent beginning of a new chapter in its life as a black hole.
The constellation Orion. Rigel is located in the lower right corner of the constellation.
Image Credit: Simon Godfrey - Unsplash
What is a Black Hole?
First predicted in Einstein’s theory of general relativity, a black hole is an object with incredible mass that has been squeezed into a tiny region of space. Its mass makes its gravitational pull so strong that nothing, not even light, can escape its pull beyond a certain point called the event horizon. As they feed off of matter around them, black holes grow larger. Since light cannot escape their gravity, black holes are invisible. While you cannot see a black hole itself, you can see how a black hole affects the space around it. For instance, a nearby star might be torn apart by a black hole’s gravity. Black holes also emit gravitational waves and radiation which precise instruments like the Laser Interferometer Gravitational-wave Observatory (LIGO) can detect.
The Corpse of a Star
Not every star becomes a black hole. When a large star with twenty or more times the mass of the sun runs out of nuclear fuel and can no longer support itself, it explodes in a supernova, emitting unimaginably bright light and gamma rays, the most powerful known form of radiation. The star’s gravity causes it to collapse into itself, and its mass is condensed into a tiny region of space. In that spectacular display, a black hole is born.
An artist’s rendition of a supernova.
Image Credit: NASA - Flickr
Types of Black Holes
Black holes range in size from miniscule pockets of space on par with a cell to massive behemoths billions of times larger than the sun. There are four main types of black holes, though not all of them have been discovered yet. They are listed in order of size from smallest to largest.
Primordial black holes would have formed soon after the Big Bang from the raw material emitted by the explosion. Most would have evaporated, but primordial black holes with larger masses may still exist. However, they are still yet to be discovered.
Stellar black holes form from supernovae. Most are around five to ten times more massive than the sun, but LIGO has detected stellar black holes up to one hundred times more massive than the sun.
Intermediate black holes have sizes between those of stellar black holes and supermassive black holes. Scientists originally thought black holes were either very large or very small, but recent research has revealed that intermediate black holes (IMBHs) may exist. They could form from stars in a cluster colliding with each other. Later, several IMBHs could merge and fall together in the center of a galaxy to form a supermassive black hole. In 2014, astronomers detected what they thought was an IMBH in the arm of a spiral galaxy, and in 2018, research led scientists to believe that intermediate black holes could lie at the centers of dwarf galaxies. However, no intermediate black holes have been conclusively detected.
Supermassive black holes have masses ranging from millions to billions of times the mass of our sun and appear to lie at the center of almost every galaxy, including our own. Scientists are trying to figure out how such massive structures form. Some ideas include multiple small black holes merging or star clusters, large gas clouds, or even large clusters of dark matter collapsing together. Dark matter is a mysterious substance that can be observed because of its gravitational effect, but scientists know very little about it because it cannot be directly observed and does not emit light.
The first real image of a black hole, taken in 2019. It is a picture of the supermassive black hole at the center of Messier 87, a huge galaxy in the constellation Virgo.
Image Credit: Event Horizon Telescope Collaboration
How Black Holes Are Studied
With the right tools, scientists can study black holes despite their elusive nature. Scientists can detect the radiation emitted by black holes, their gravitational waves, and powerful jets of material spewed into the inky depths of space. Here is a list of organizations that study black holes:
Event Horizon Telescope Project
National Science Foundation (NSF)
NSF’s Laser Interferometer Gravitational-wave Observatory (LIGO)
NSF’s National Radio Astronomy Observatory (NRAO)
UCLA Galactic Center Group
Could a Black Hole Destroy Earth?
Earth is not in danger of being destroyed by a black hole. There are no black holes close enough to pose a threat, and the sun could never become a black hole because it is not big enough. Instead, as the sun grows older, it will become a red giant and expand to swallow the inner terrestrial planets. Then, it will shed off its outer layers and become a white dwarf only slightly larger than Earth.
As a star like our sun sheds off its outer layers and becomes a white dwarf, it leaves behind a mass of gas and dust known as a nebula.
Image Credit: NASA - Flickr
A Journey Into the Abyss
Let’s venture into the great unknown and imagine ourselves diving into a black hole. For this journey, you will bring a close friend or relative with you. For the purpose of this simulation, we will ignore the multitude of reasons why you would not have this opportunity or survive this experience--at least not in the near future.
As you and your companion wait outside the black hole, you can already feel the gravity of the hungry behemoth tugging you toward it. The accretion disk swirls and sparks brightly with a kaleidoscope of colors. The black hole spews brilliant jets of plasma perpendicular to the accretion disk into the dark depths of space.
You exit your spaceship and venture through the vacuum of space towards the gaping maw of the black hole while your companion watches from the spaceship. As your companion sees you move closer to the black hole, they take out a watch and observe the time as it ticks. Back in your house on Earth, the clocks are actually ticking faster than the watch is ticking for you and your companion! The two of you are experiencing time slower, one of the bizarre effects of the black hole’s incredible gravity on the very fabric of space-time. In reality, any massive body, including Earth, has this effect, but the planet’s gravity is too weak for this to be noticeable without the most precise of instruments.
Your companion watches as you move closer and closer to the black hole. As they watch, you seem to slow down, a result of the same slowing of time discussed earlier. You watch eagerly--or perhaps fearfully--as you approach the event horizon. Anything that travels beyond this boundary has no chance of escaping the black hole’s immense gravity. And now you’ve just crossed that point of no return.
From your companion’s perspective, you appear to be perpetually frozen in time at the edge of the black hole because of how much time has slowed down. From your perspective, you have entered the black hole. What happens next?
Scientists don’t know for sure because no information can leave a black hole once it has entered. A popular idea is that the gravity of the black hole would stretch and elongate your body like a noodle in a process called spaghettification. However, a 2012 study suggests that quantum effects would cause the event horizon to act much like a wall of fire and instantly burn you to death. A more wild proposition is that black holes are the doors to a parallel universe!
When you return home, you are shocked to see that many years have passed while you were visiting the black hole. Your friends and family may be old or whole generations might have passed depending on how long you were gone. Everyone at home is equally amazed to see that you and your companion haven’t aged a day. All of you agree that there is much to learn from your truly one of a kind experience.
No matter how you look at them, black holes are mind blowing and breathtaking. They push at the seams of reality and make us question what we thought we knew was solid fact. Even with years of meticulously gathering and analyzing data, there is still so much about these gravitational wonders that remains a mystery. Black holes embody the spirit of
science--scientists will probably never completely unravel the mystery, but they will do their best to come as close as they possibly can to understanding their secrets. No matter where the research takes us, there is no doubt that it will be a thrilling journey.
Afternote
Here’s a space joke to brighten your day!
How do you organize a space party?
You planet!
--Zach Vanderbosch, UT Austin
Works Cited
“Exploring Black Holes.” Exploring Black Holes | National Science Foundation, National
Science Foundation, www.nsf.gov/news/special_reports/blackholes/.
Howell, Elizabeth. “Rigel: Orion's Brightest Star.” Space.com, Space, 18 Mar. 2019,
May, Sandra. “What Is a Supernova?” NASA, NASA, 1 June 2015,
www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-
supernova.html.
Redd, Nola Taylor. “What Are Black Holes?” Space.com, Space, 11 July 2019,
Vanderbosch, Zach. “When I Look up and See the Milky Way Galaxy, Am I Looking towards
the Center of the Galaxy or towards Outer Space?” Ask An Astronomer, 2 Oct. 2015,
askanastronomer.org/galaxies/2015/10/02/looking-at-the-milky-way/.
“What Are Black Holes?” --Universe Forum--Black Holes--What Are They?, 2004 Smithsonian
Institution, 2004, www.cfa.harvard.edu/seuforum/bh_whatare.htm.
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