Well, once again, the random number generator has selected a location in the constellation Cetus. Instead of, like usual, just mocking this constellation for not looking like anything even though it's supposed to represent a sea monster or a whale or something, I decided to try to give it another chance and took another look at it, and it's actually more disappointing than I first thought. Instead of just looking like a bunch of randomly-distributed stars, it's actually a bunch of randomly-distributed really faint stars, although people can play connect-the-dots with those faint stars to make a smll polygon connected by a line to a larger polygon, which would very vaguely make it look like a plesiosaur, if you can actually see the stars.
The specific object that this episode's coordinates point to is a complex system named PMN J0134-0931. The letters PMN stand for Parkes-MIT-NRAO, one of the astronomical catalogs (but not the first) that listed radio data for this object [1], while the digits indicate the coordinates and the J indicate that these are the coordinates in the system set up in the year 2000.
So, this object was detected as a radio source in 1970 in something called the Ohio Survey between Declinations of 0° and 36° South [2]. In the rest of the twentieth century, it would only appear in four more science papers, including one of the papers published in 1994 about the Parkes-MIT-NRAO survey [1]. It really did not attract that much attention at all. Then, in 2002, two different groups of people working with the Very Large Array separately discovered that PMN J0134-0931 is a system containing a gravitationally lensed quasar [3, 4]. Very interestingly, both of their papers, one of which had Michael D. Gregg as the first author and one of which had Joshua N. Winn as the first author, were published in the same issue of the Astrophysical Journal.
So, to begin with, a quasar by itself is a type of active galactic nuclues (AGN) with a supermassive black hole in its center, a disk of hot, gravitationally-compressed gas falling towards that black hole, and very hot jets of ionized gas appearing above the poles of that black hole. The jets are basically produced by gas from the disk that was deflected away from the black hole by its magnetic fields. Quasars are a specific situation where the jets are kind of tilted towards the Earth, so all of the electromagnetic radiation from the objects looks relatively point-like.
That's the simple part about the system PMN J0134-0931, but what makes the quasar in this system special is that it is located behind another relatively faint galaxy. The gravitational forces from the galaxy in front, which is at a distance where the light has traveled about 6.7 billion years to reach the Earth [5], are distorting the electromagnetic radiation (including visible light) from the quasar, which is at a distance where the light has traveled 10.7 billion years to reach the Earth [3]. This type of system is called a gravitational lens.
When the discovery that PMN J0134-0931 was a gravitational lens was published in 2002, the number of known gravitationally lenses was very small, so it was quite exciting to find a new one. Additionally, the light from the lensed quasar was actually distorted into what is called an Einstein ring. This is when the gravitational lensing causes the background object to look sort of ring-like. The quasar in the background in the PMN J0134-0931 system actually appears in two different locations on either side of the nearby lensing galaxy, with the radio emission on one side appearing as two small dots that are very close together and the radio emission on the other side appearing as a longer arc-like structure [4]. The emission in other bands, such as the visible and near-infrared parts of the electromagnetic spectrum, look similar, but the images are not as sharp, and this is because advanced observing and imaging techniques could be applied to map the radio emission but not the emission in other bands [3, 4, 5, 6]. Interestingly, no one seems to have published any images showing what the galaxy in front of the quasar looks like. The quasar in the background is apparently so bright that it produces severe glare when anyone tries to image the foreground galaxy.
As I said before, gravitational lenses seemed really rare back in 2002. I was not able to find a good reference for the exact number of known Einstein rings as of that year, but I would guess that it is a number smaller than what I can count on both of my hands. In contrast, we know about many, many more gravitational lenses these days, in large part because a lot of newer surveys, particularly surveys in the far-infrared by the Herschel Space Observatory which operated from 2009 to 2013, have detected quite a few of these things [7]. For example, my next science paper features at least 6 objects that look like Einstein rings and a couple more that look very suspiciously like they are also gravitationally lensed. So, by today's standards, PMN J0134-0931 might not be quite so exciting these days, but it's still something that people are studying.
Gravitational lenses can be used for one of three basic purposes. First, observational data for the systems can be used to study the object in the foreground, mainly by how it affects the light coming from the background object [8]. Second, the data can be used to study the object in the background, particularly since the gravitational lensing will not only bend the light but also make the light from the background source appear brighter and therefore make it easier to see the background object, even though it will look distorted [9, 10 ,11]. Third, the systems can be used in a few different ways to make various measurements of cosmological parameters that describe the formation and expansion of the universe [12, 13, 14, 15, 16, 17, 18, 19].
In the case of PMN J0134-0931, most of the papers that focused on just that system seem to have chosen option one. They have been most concerned with trying to understand the object in the foreground by identifying its effect on the light from the background quasar. In many gravitationally lensed systems, people would use the distortion of the light from the background object to search for dark matter in the foreground object, but in the PMN J0134-0931 system, they have been looking at how different elements and molecules have been aabsorbing light from the background quasar [5, 20].
Among other things, this approach has allowed astronomers using the Atacama Large Millimeter/submillimeter Array to find interstellar molecular gas in the foreground galaxy [20]. This result, which was published in 2018, was a notable technical achievement in an of itself, as it had only been done previously in four other objects []. However, it also demonstrated that the object in the foreground is probably a disk-like galaxy containing a lot of interstellar gas [], which means that it has the potential to form a lot of new stars out of all of that gas. This type of observational result gives us a lot of new information about a galaxy that we would not know is there if it weren't for how it was lensing the light behind it, and this is one of the reasons why gravitational lenses are so exciting that people are going to continue to observe them. Not me, though; I'm more interested in the objects in the background in these gravitationally lensed systems.