Kraken in the Milky Way by William Lama, Ph.D.
Kraken in the Milky Way
by William Lama, Ph.D.
NASA image
As a young kid I was fascinated by the “old folks.” Grandpa Lama came to America in 1902, leaving his wife and infant daughter behind in Naples. He worked as a “fireman” on the NY Central Railroad for three years, before earning enough to send for his family. In fact, my grandparents on both sides emigrated from Italy around the turn of the century. They lived through two world wars and the Great Depression, yet were eternally optimistic and thankful.
Most Sundays we had dinner with the grands: insalata mista, macaroni with grandma’s sauce, pollo arrosto, mixed nuts and pie ala mode. The table was always overflowing thanks to John Lama and Sons, our grocery business. I began working there at age eight. I would open doors for customers and offer to carry out bags of groceries. Whenever I received a compliment my Mom’s standard reply was: “Well, you don’t think he came out that way.” No indeed! My parents, all the aunts and uncles, neighbors and the Sisters of Saint Joseph all played a part in my formation.
Which brings me to the subject of this essay, galaxy formation. Last month (“Life is Grand in Palos Verdes, USA”) I described our heavenly home, the Milky Way Galaxy. Well, you don’t think it came out that way. The Milky Way galaxy that contains our Solar System began forming roughly 13.6 billion years ago, about 0.2 billion years after the Big Bang. (“Big Bang Cosmology – Believe it or Not,” Palos Verdes Pulse, May 2020) Today the Milky Way contains over 100 billion stars. Our Sun is one of many.
So, where did they all come from? A team of astrophysicists have been using Ancestry.com to reconstruct the cosmic ancestry of our galaxy. I’m just kidding. They actually used artificial intelligence to figure out the Milky Way family tree.
The scientists who derived the Milky Way story used computer simulations called E-MOSAICS to show how the Milky Way evolved as it cannibalized smaller galaxies. That’s right. Our Milky Way grew up by gobbling nearby galaxies, as illustrated in the following figure.
Galaxy merger tree of the Milky Way. "Kraken reveals itself – the merger history of the Milky Way reconstructed with the E-MOSAICS simulations," J. M. Diederik Kruijssen et al, Monthly Notices of the Royal Astronomical Society. The vertical scale on the right gives the time before present in billions of years. (Gyr) The color coded horizontal scale gives the masses of the progenitor galaxies in multiples of the mass of the Sun. Data from the Gaia space probe. Gaia is currently building the most precise 3D map of the stars in the nearby Universe.
Using Gaia data, Kruijssen et al accurately predicted four known mergers in the Milky Way's past as well as the previously unknown merger with a galaxy called Kraken. These main progenitor galaxies are connected to the trunk of the Milky Way tree. The colors represent their stellar mass in multiples of the Sun’s mass. From left to right, the six images at the top are the progenitor galaxies: Sagittarius, Sequoia, Kraken, Helmi and Gaia-Enceladus. The black lines linked to the family tree show when the collisions occurred in billions of years before present.
The earliest collision with Kraken (11 billion years ago) was "the most significant merger the Milky Way ever experienced."
Collision with Kraken, artistic rendition, Getty Image
According to the Norse Sagas, the Kraken is a legendary cephalopod-like sea monster of gigantic size that dwells off the coast of Scandinavia and terrorizes sailors. More recently Kraken was featured in Marvel Comics and in the movie Clash of the Titans.
Another galaxy-altering merger will occur in the future, when the neighboring Andromeda galaxy (currently 2.5 million light-years away) collides with the Milky Way. The monster collision will occur about 4.5 billion years from now, according to research based on observations made by Europe's Gaia spacecraft.
The following figure is a prediction of the merger between Andromeda and the Milky Way. Also shown is Triangulum, a smaller nearby galaxy that will pass by in 2.5 billion years.
Predicted trajectories of three galaxies. European Space Agency.
Returning to our story of collisions past, Professor Kruijssen concludes: Our results add to a growing body of evidence that the Milky Way experienced an unusual path to adolescence. Not only did it assemble unusually quickly, but it also experienced a striking paucity of major accretion events (the five in the figure). It may not be the most representative example for understanding the evolution and assembly of galaxies, but is a correspondingly more pleasant environment to live in.
Postscript. In the days before Christmas many of us hoped to get glimpse of the “Bethlehem Star.” We were told that it would be a rare sighting, visible only every 20 years, or was it every 300 years? Tune in next month for the rest of the story.
Life is indeed grand in the Milky Way Galaxy, Palos Verdes Peninsula.
Dr. William Lama has a PhD in physics from the University of Rochester. Taught physics in college and worked at Xerox as a principle scientist and engineering manager. Upon retiring, joined the PVIC docents; served on the board of the RPV Council of Home Owners Associations; served as a PV Library trustee for eight years; served on the PV school district Measure M oversight committee; was president of the Malaga Cove Homeowner's Association. Writes about science, technology and politics, mostly for his friends.
email: wlama@outlook.com