“A woman on a mission, quite familiar with quasars
Her heart is in the kitchen but her soul is in the stars
Crystal clear on logic but short on expertise
This is a very ancient puzzle, she feels herself a piece”
– Jimmy Buffett, “Desdemona’s Building a Rocket Ship”
Jimmy Buffett’s song “Desdemona’s Building a Rocket Ship” is actually based on a character from his novel Where Is Joe Merchant? (Yes, Jimmy Buffett is a published author, not just a singer and songwriter.) Desdemona is a psychic who believes she is called to travel to the Pleiades, a star cluster located in the Taurus constellation. She starts to study astronomy and begins to build a “rocket ship” she names the Cosmic Muffin, but she lacks the technical skill to finish the ship. As the song claims, Desdemona is “quite familiar with quasars.”
So what is a quasar?
In 1932, physicist Karl Jansky was studying disruptions to radio telephone communications. He discovered that some of the natural disturbances came from radio waves emitted by the Milky Way, the galaxy where we reside. By the 1950s, astronomers were surveying the sky for radio waves in the hopes of understanding more about the universe. Many radio waves were identified as originating from galaxies, but some radio sources appeared to come from bright star-like structures. Astronomers called these mysterious points “quasi-stellar radio sources,” because they resembled stars and the radio signals came from a single point. Eventually this was shortened to “quasar.”
For a while, astronomers couldn’t figure out what these objects were. Quasars had odd spectra- the ranges of wavelengths of light detected. Spectra are keys to funding the object’s composition, and nothing seemed to match up with quasars, which looked like stars but had very different spectra than stars. In 1963, Dutch American astronomer Maarten Schmidt realized that the spectra were so strange because the quasars were so far away and the light was redshifted– that is, the wavelengths are stretched longer as the object (a quasar in this case) moves away from our observation point on Earth. We could only see quasars because they were exceptionally bright, emitting massive amounts of energy. Quasars are so bright that they shine 10 to 100,000 times brighter than the Milky Way.
It took some time to figure out how quasars could be so bright. Today, a quasar is thought to be made of a supermassive black hole surrounded by an accretion disk. A supermassive black hole is an area with an incredibly high density and amazingly strong gravitational field. Within a quasar, the gravitational field of the supermassive black hole pulls in gas from a surrounding accretion disk. This “disk” is a flat structure composed of gas that spirals inwards towards the supermassive black hole.
If you’ve read up on black holes before, you know that they cannot be observed directly, as anything that falls into a black hole never escapes, including light. However, if the matter does not cross over the boundary of the black hole (called the event horizon), it could be accelerated. As the matter moves faster, it heats up, and friction between the particles would give off energy. This energy is released as electromagnetic radiation, including radio, infrared, visible, ultraviolet, and X-ray wavelengths.
These light waves take billions of years to travel through space to us, so we’re effectively looking at past quasars. The closest observed quasar is about 600 million light-years from Earth. (One light-year is approximately 9.5 trillion kilometers, or 5.9 trillion miles.) Light from the farthest observed quasar took 12.9 billion years to reach us. (The farthest quasar is approximately now 29 billion light-years away from us now, as the universe is expanding and the quasar is moving away. It would now take light longer to reach us than it did previously.) Based on the distance of observed quasars and the amount of time it takes for the light to reach us, most of the observed quasars were actually active 9 to 13 billion years ago, and there are relatively few active now. While a quasar becomes inactive, the black hole remains. In theory, a quasar could start up again once the black hole is given another accretion disk to “feed” from.
So there you go. Even if you don’t know as much as Desdemona, hopefully you learned a little bit about the basics of quasars.
Keep calm and science on.