I once accidentally photographed one of the most important stars in the universe…
This star highlighted in the photo is called M31_V1 and is located in the Andromeda Galaxy. Andromeda – AKA M31 – is the closest galaxy to our Milky Way. But previously it was known as a galaxy, it was called the Andromeda Nebula. Before this particular star in Andromeda was studied by Edwin Hubble, the namesake of the Hubble Space Telescope, we didn’t really know if there were other galaxies. even existed. Think about it! Recently, as a hundred years ago, we thought that the Milky Way could be the whole universe. Even then… it’s pretty big. The Milky Way is about 150,000 light-years across. A light year is about 10 TRILLION kilometers, so even at the speed of light it will take almost as much time to cross the Milky Way as humans existed on planet Earth. M31_V1 changed all that.
This star in Andromeda is marked “V” because it is known as Cepheid variable. Cepheid variables can be used as a “standard candle” to measure distances in the universe. We generally know how to get bright variable stars. So, if we compare two of them, and one is much dimmer than the other, we can conclude that it is further in space. In 1924, using this technique, Hubble measured the light of V1 and the next 35 variable stars to measure the distance to Andromeda in an incredible 900,000 light-years … far too far to be part of our own galaxy. I didn’t realize I had captured the same star in my field of vision until Dr. Howard Trottier, who founded the SFU Trottier Observatory, where I was taking pictures, pointed it out.
Thanks to advanced imaging techniques and more accurate measurements, we know that Andromeda is 2.4 million light-years behind. But the Hubble value of 900,000 years was enough to reveal that our galaxy was just one “island universe” in a much larger universe. And how many galaxies are there? Andromeda and I knew at least two. But since then we have discovered that there are not two, nor ten, nor hundreds, nor thousands, nor millions, but probably TRILLIONS of galaxies, each filled with hundreds of billions of stars. Our own Milky Way is a set of between 100-400 billion stars (we are in orbit one their). There are probably more stars in the universe than grains of sand on all the beaches on Earth. But how can we know? So because Hubble was measuring several variable stars in a single galaxy at the time, the Sloan Digital Sky Survey released a new map on July 19 that is the most complete picture of the universe ever made. Twenty years have passed and it contains 4 MILLION fixed galaxies !!
Each of these points in the image is not a star, but a GALAXY filled with stars. Using a specialized telescope in New Mexico, Sloan Digital Sky Survey has created a series of catalogs of distant galaxies to create this map of the universe. The catalogs contain large red (older) galaxies closer to the Milky Way, more distant blue (younger) galaxies, and the most distant are galaxies, the central supermassive black hole – which we believe is in the core of most galaxies – is actively fed by dust, gas and stars. . These nutrient coals can become the brightest objects in the universe, known as quasars. The shape of the fan image shows regions where we are limited to observations due to dust and gas in our own Milky Way galaxy, which obscures our view of parts of the universe.
Hubble made another incredible discovery. Denoted as Hubble Constant, Hubble realized that distant galaxies were moving far away from us. This was the first evidence that our universe was actually expanding. The extension itself can be used to measure the distance from these galaxies. SDSS uses different methods than those used to measure the distance to Andromeda. A standard candle like the Cepheid variable works in the order of millions of light years, but we cannot solve individual stars in very distant galaxies. Instead, SDSS measures the “redshift” of the galaxy. When light from a distant galaxy travels through space, it moves across the expanding universe and literally stretches the light, causing it to redden. The amount of red that has displaced the light, by the time it reaches us, gives us an idea of how far the light has traveled.
Tracking these galaxies also helps track the expansion of the universe over time as the movie launches back. We call the “review of time back” the farther into the space we are looking for, the farther back in time we see the time it takes for light from a distant universe to reach us. For example, imagine if I sent you a picture of me, but it took the post office twenty years to get to you because I was so far away. You see me the way I appear twenty years ago. Similarly, the SDSS map looks back about 400,000 years after the birth of the universe and how it has expanded over time. Until recently, a large gap in this time scale existed in the middle of 11 billion years between the ancient Russian past and present (a large gap, taking into account the universe, is 13.8 billion years). This gap was filled by the latest SDSS catalog called eBOSS (extended study of Baryon oscillations on oscillations). In addition to having a new map of the universe, SDSS fills in pieces to another final question … why and how is the universe expanding? Currently, the “force” that causes the expansion of the universe is called the mysterious and unknown “Dark Energy”. The new map helps determine if the effects of Dark Energy have changed over time. Based on SDSS measurements, it seems that the rate of expansion of the universe in the history of the universe is different, which may be a clue as to how Dark Energy works. Therefore, potential discoveries that will help us better understand dark energy are made possible by SDSS cards.
And now the flight through space and time. LEAD, a tour of the universe !!
Interview with the joint SDSS team https://youtu.be/TKiYOnsE8Y4
University of Waterloo press release: https://uwaterloo.ca/astrophysics-centre/news/astrophysicists-release-largest-3d-map-universe-ever-create
SDSS press release: https://www.sdss.org/press-releases/no-need-to-mind-the-gap/