I WONDER…

• If some black holes are created by the collision of stars, would there be a similar outcome if galaxies collided? How could this affect the Milky Way?

 

For many years, scientists have been exploring the laws of our continuously expanding universe as well as the things that lie beyond our galaxy. After extensive research, we have determined that Albert Einstein’s theory of general relativity provides strong theoretical support for the existence of black holes that can be formed by the collision of some stars. Along with that, in 1924, Edwin Hubble discovered the Milky Way is not the only galaxy in our universe. This leads me to my fascinating scientific question: How do the outcomes of star collisions compare to those of galaxy collisions? 

 

What Is A Black Hole?

Black holes are one of the most mysterious objects in space. They have been studied for a long time, yet are still not fully understood. Their name, “black holes,” can be misleading, because they are not actually holes, they are extreme concentrations of matter packed into incredibly small spaces. Due to their immense density, they generate powerful gravitational fields, with their event horizon. An event horizon marks the boundary around a black hole where the escape velocity surpasses the speed of light, preventing anything from escaping. Since black holes are often envisioned as spherical, the intensity of their gravitational field depends on both its mass and volume. The greater the mass and the smaller the volume results in a higher density and an even stronger gravitational pull around its surface. This concludes the statement that black holes are so intensely dense that they do not even allow light (which has no mass and travels 299,792,458 meters per second) to escape. As well, the bigger the black hole is in space, the cooler it is in temperature.

Black holes vary in mass and range from can be a billion times the mass of our Sun. They are categorized into three different groups:

• Stellar black holes—Most common and is around  10 times the mass of our Sun.
• Intermediate black holes—Falling between stellar and supermassive in size.
• Supermassive black holes—Found at the core of most galaxies and can be billions of times heavier than the Sun.

*Watch this short video from NASA to learn more about black holes!*

 

How Are Black Holes Made In Space?

In 1916, Karl Schwarzschild — a German physicist and astronomer developed the idea from Albert Einstein’s theory of general relativity that black holes do exist all throughout the universe. The spherical objects can be created in several different ways. In the simplest explanation, black holes are made when…

• Stars reach the end of their lives and implode, basically collapsing in on themselves.
• The second way for a black hole to form is when pairs of stars explode, turning into two separate black holes.
• And the third scenario is when neutron stars collide together, creating an even bigger neutron star that has the possibility of collapsing into itself and creating a black hole.

My primary focus for this project will be on the formation of a black hole resulting from the collision of stars. An interesting fact about these stars colliding is that they do not only become a black hole, they can create very precious metals such as uranium and even gold and silver.

 

Understanding Star Collisions And Neutron Stars

Neutron stars are not just any ordinary star, they are actually the leftover core of a big star after it explodes. Its components are a solid outer crust, and beneath are superdense liquids, filled mostly with neutrons. When massive stars burn up all their fuel, they explode in a supernova, which is an explosion of a star that is so luminous and powerful. The remnants left over depend on how big the original stars were. It will become a neutron star if the original stars were 7–19 times bigger than our Sun, and it will become a black hole if it was over 20 times bigger.

A neutron star merger happens when two neutron stars collide. First, they circle each other, slowly getting closer as they lose energy by sending out invisible gravitational waves. Black holes can form not only from the collision of regular stars but also from the collision of neutron stars. Their combined amount of mass has the possibility to create such a strong gravity which causes them to collapse into a black hole.

An interesting fact about neutron stars is that they are made up of the densest material that we can physically observe. Unlike black holes, neutron stars do not have an event horizon — allowing us to see into it. These stars can be as small as a city in diameter, but contain double the mass of our Sun all packed into a small sphere. As well, special neutron stars, named pulsars send out beams of light that look like flashes as they spin. After a long period of time, they can pulse with such precision that they are even more accurate than an atomic clock. Similar to many cosmic objects in space including planet Earth, neutron stars have a magnetic field and are in fact the strongest known magnets! 

 

The Components Of Galaxies

One of the most groundbreaking scientific discoveries of the 20th century was Edwin Hubble’s unveiling that the universe extends beyond the Milky Way and is filled with countless other galaxies. His findings forever changed our knowledge of the space, leading us toward a deeper understanding of the Big-Bang Theory. Galaxies are so interesting! They are filled with a combination of stars, planets dust and dark matter. These components of a galaxy stay together because the force of gravity pulls them all together. A cool fact about galaxies is that many contain supermassive black holes at their core. Galaxies are found scattered all across our Universe, and are often seen in clusters. There are different components that make up a galaxy:

• Size of galaxy—Measured in light years (Light travels incredibly fast, about 186,000 miles or 300,000kilmeters every second).
• Its mass—The mass of a galaxy is measured using the unit solar mass (mass of our Sun). All galaxies have different masses. 
• Temperature—Most galaxies do not have a very hot temperature. The objects within a galaxy may be different in temperature, but the space around them is cold, making galaxies an average temperature. 
• Its characteristics—All galaxies look different because of their contents and materials that make up the galaxy. There are Spiral Galaxies (look like starry whirlpools with a bright center and bluish tint) as well as Elliptical Galaxies (more round and tend to be red). It is also possible for galaxies to have spiral arms, dust trails and rings.

 

The History And Facts About Our Milky Way

Planet Earth is home to the Milky Way Galaxy. Ancient Greeks named it “galaxies kuklos” (milk circle), a term later changed by the Romans, who gave it the name we currently know as the “Milky Way.” NASA has discovered that the Milky Way consists of more than half a million stars! Interestingly, it is a mostly flat and slightly warped galaxy with a dense center and curved arms of gas and stars. Our solar system is just one of over 500 other solar systems within the galaxy. A cool fact about the Milky Way is that there actually lies a supermassive black hole at the center, called Sagittarius A. Astronomers can’t see this object directly because it’s hidden by dust and gas, but by tracking nearby stars and gas clouds, they’ve determined its massive size. The Milky Way is also surrounded by a vast halo of invisible dark matter, acting like cosmic glue that keeps stars from flying away. According to National Geographic, the Milky Way will collide with its neighbor, Andromeda Galaxy in around 2-4 billion years. Surprisingly, the Milky Way is actually a product of Sagittarius Dwarf and the Triple Galaxy that merged together a long time ago. This discovery of our Milky Way and galaxies merging leads me to my question… What happens when galaxies collide?

*If you are curious about our solar system within the Milky Way, watch this video from National Geographic!*

 

When Galaxies Collide

Galaxies are quite fascinating! When they collide, it takes millions of years for them to complete their merge, due to gravitational forces pulling them together. This causes them to pass through each other multiple times before actually fully combining. In able for galaxies to merge, they need to be pretty close to each other, otherwise gravity will not force them together. Interestingly, a big galaxy can stretch a smaller one without much change to itself, but when two similar sized galaxies collide, they release matter, create brand new stars and change in structure.

During the collision—Mutual attraction slowly draws galaxies into contact. The physical shapes of the galaxies become very distorted because of gravitational forces. Their arms get stretched out, creating abstract patterns and tidal tails (long stream of stars, gas and dust). Next gas clouds made of hydrogen gas compress. The intense increase of friction leads to bursts, which are the beginning of new stars.

Outcome of the collision—If both the galaxies that collided were very similar in proportion, they are able to become a large Elliptical Galaxy, causing them to reshape and lose their original spiral like structures. While it is pretty rare for individual stars to collide during the merge of galaxies, some stars are actually flung out or interact with supermassive black holes. Long term changes of the collision occur. The combination of two galaxies creates beautiful cosmic evolutionary changes in space, changing the structures and dynamics within the universe.

 

Star Collisions VS. Galaxy Collisions

This research raps up my scientific question: “If some black holes are created by the collision of stars, would there be a similar outcome if galaxies collided? How could this affect the Milky Way?”

As you can see, the outcome of stars colliding and galaxies colliding are much different from each other. When stars collide, they have the possibility of creating black holes. While when galaxies collide, they merge together and create a combination of the two galaxies. Regarding the merge of the Milky Way and Andromeda Galaxy that was mentioned earlier, the two galaxies are expected to collide in a few billion years! NASA states that their spiral shapes will be changed, and by 6 billion years merge into a single Elliptical Galaxy. Since the Triangulum galaxy is also nearby, it may continue orbiting the merged galaxy. Some models also predict that it could join the collision. Considering this collision has yet to occur, it remains uncertain whether it will impact Earth directly or influence the future of human life.

 

Citations: 

Research:

Canadian Space Agency. (2020, March 12). Fact sheet: Galaxy. https://www.asc-csa.gc.ca/eng/astronomy/fact-sheets/galaxy.asp

Collins, G. W. (2021). Black Hole. Go. https://go-gale-com.bc.idm.oclc.org/ps/retrieve.do?tabID=Reference&resultListType=RESULT_LIST&searchResultsType=MultiTab&retrievalId=07ceb211-5887-427f-b4e6-16deed5e3c95&hitCount=7&searchType=BasicSearchForm&currentPosition=2&docId=GALE%7CCX8124400350&docType=Topic%2Boverview&sort=Relevance&contentSegment=ZXAR-VRL&prodId=SCIC&pageNum=1&contentSet=GALE%7CCX8124400350&searchId=R6&userGroupName=bcdc&inPS=true

Drake, N. (2018, January 12). 10 weird things you (probably) didn’t know about the milky way. Science. https://www.nationalgeographic.com/science/article/milky-way-galaxy-facts-black-hole-stars-space-science

Eicher, D. J. (2023, May 18). What happens when Galaxies Collide?. Astronomy Magazine. https://www.astronomy.com/science/what-happens-when-galaxies-collide/

Harvard & Smithsonian. (n.d.). Galaxies – merging and interacting. Galaxies – Merging and Interacting | Center for Astrophysics | Harvard & Smithsonian. https://www.cfa.harvard.edu/research/topic/galaxies-merging-and-interacting

Images:

Labster.com. (n.d.). The gravitational field (IMAGE). Labster. https://theory.labster.com/the_gravitational_field/

NASA, ESA, and F. Summers (STScI); Simulation: NASA, ESA, G. Besla (Columbia University), and R. van der Marel (STScI). (2012, May 31). The fate of the Milky Way, Andromeda and Triangulum Galaxies (Annotated) | HubbleSite. Bing. https://www.bing.com/images/search?view=detailV2&ccid=YKgipq0q&id=5C8F71B38CA0F7F8F5A16E58CC588D59BDDA9E77&thid=OIP.YKgipq0qjjvcu67XyMifWgHaEK&mediaurl=https%3A%2F%2Fstsci-opo.org%2FSTScI-01EVSKPVG7NYWST6F4VD34C3A4.jpg&cdnurl=https%3A%2F%2Fth.bing.com%2Fth%2Fid%2FR.60a822a6ad2a8e3bdcbbaed7c8c89f5a%3Frik%3Dd57avVmNWMxYbg%26pid%3DImgRaw%26r%3D0&exph=1080&expw=1920&q=milky%2Bway%2Bgalaxy%2Bwith%2Bandromeda%2Bgalaxy%2Band%2Btriangulum%2Bgalaxy&simid=608008984703293599&form=IRPRST&ck=394FADE18CB61DC2ED0CA3D31B91365E&selectedindex=0&itb=0&cw=1334&ch=657&ajaxhist=0&ajaxserp=0&vt=0&sim=11