(CNN)Astronomers have detected the most massive neutron star ever, and it almost shouldn't even exist.
Neutron stars are the smallest in the universe, with a diameter comparable to the size of a city like Chicago or Atlanta. They are the leftover remnants of supernovae. But they are incredibly dense, with masses bigger than that of our sun. So think of the sun, compressed into a major city.
Photos: Wonders of the universe
This illustration shows a massive star on the brink of explosion.
Hide Caption
1 of 57
Photos: Wonders of the universe
Meet the fastest asteroid in our solar system, which zips around the sun every 113 days. This artist's rendering shows the asteroid 2021 PH27 (top right) and Mercury (below) orbiting the sun.
Hide Caption
2 of 57
Photos: Wonders of the universe
A ghostly set of X-ray rings were found around a black hole with a companion star. These rings are created by light echoes.
Hide Caption
3 of 57
Photos: Wonders of the universe
This image, taken with the Atacama Large Millimeter/submillimeter Array in Chile, shows the PDS 70 system 400 light-years away. This planetary system is still forming and still in the process of being formed. One of the planets in the system has a moon-forming disk around it.
Hide Caption
4 of 57
Photos: Wonders of the universe
This image shows supernova 2018zd (pictured as the large white dot on the right), a new type of supernova called an electron capture. To the left is the galaxy NGC 2146.
Hide Caption
5 of 57
Photos: Wonders of the universe
This image from the STARFORGE simulation shows the "Anvil of Creation," a giant gas cloud with individual stars forming inside of it.
Hide Caption
6 of 57
Photos: Wonders of the universe
Astronomers used NASA's Chandra X-ray Observatory to study the supernova remnant Cassiopeia A and discovered titanium, shown in light blue, blasting out of it. The colors represent other elements detected, like iron (orange), oxygen (purple), silicon (red) and magnesium (green).
Hide Caption
7 of 57
Photos: Wonders of the universe
The supermassive black hole at the center of the M87 galaxy, the first to ever be imaged, can now be seen in polarized light. Swirling lines reveal the magnetic field near the edge of the black hole.
Hide Caption
8 of 57
Photos: Wonders of the universe
This image from the Sloan Digital Sky Survey shows the galaxy J0437+2456, which includes a supermassive black hole at its center that appears to be moving.
Hide Caption
9 of 57
Photos: Wonders of the universe
This artist's impression shows how the distant quasar P172+18 and its radio jets may have looked 13 billion years ago. The light from the quasar has taken that long to reach us, so astronomers observed the quasar as it looked in the early universe.
Hide Caption
10 of 57
Photos: Wonders of the universe
This image shows the vicinity of the Tucana II ultrafaint dwarf galaxy, captured by the SkyMapper telescope.
Hide Caption
11 of 57
Photos: Wonders of the universe
These images show two giant radio galaxies found with using the MeerKAT telescope. The red in both images shows the radio light being emitted by the galaxies against a background of the sky as it is seen in visible light.
Hide Caption
12 of 57
Photos: Wonders of the universe
This artist's conception of quasar J0313-1806 depicts it as it was 670 million years after the Big Bang. Quasars are highly energetic objects at the centers of galaxies, powered by black holes and brighter than entire galaxies.
Hide Caption
13 of 57
Photos: Wonders of the universe
Shown here is a phenomenon known as zodiacal light, which is caused by sunlight reflecting off tiny dust particles in the inner solar system.
Hide Caption
14 of 57
Photos: Wonders of the universe
This artist's impression of the distant galaxy ID2299 shows some of its gas being ejected by a "tidal tail" as a result of a merger between two galaxies.
Hide Caption
15 of 57
Photos: Wonders of the universe
This diagram shows the two most important companion galaxies to the Milky Way: the Large Magellanic Cloud (left) and the Small Magellanic Cloud. It was made using data from the European Space Agency Gaia satellite.
Hide Caption
16 of 57
Photos: Wonders of the universe
The Blue Ring Nebula is thought to be a never-before-seen phase that occurs after the merger of two stars. Debris flowing out from the merger was sliced by a disk around one of the stars, creating two cones of material glowing in ultraviolet light.
Hide Caption
17 of 57
Photos: Wonders of the universe
The red supergiant star Betelgeuse, in the constellation of Orion, experienced unprecedented dimming late in 2019. This image was taken in January using the European Southern Observatory's Very Large Telescope.
Hide Caption
18 of 57
Photos: Wonders of the universe
This is an infrared image of Apep, a Wolf-Rayet star binary system located 8,000 light-years from Earth.
Hide Caption
19 of 57
Photos: Wonders of the universe
An artist's illustration, left, helps visualize the details of an unusual star system, GW Orionis, in the Orion constellation. The system's circumstellar disk is broken, resulting in misaligned rings around its three stars.
Hide Caption
20 of 57
Photos: Wonders of the universe
This is a simulation of two spiral black holes that merge and emit gravitational waves.
Hide Caption
21 of 57
Photos: Wonders of the universe
This artist's illustration shows the unexpected dimming of the star Betelgeuse.
Hide Caption
22 of 57
Photos: Wonders of the universe
This extremely distant galaxy, which looks similar to our own Milky Way, appears like a ring of light.
Hide Caption
23 of 57
Photos: Wonders of the universe
This artist's interpretation shows the calcium-rich supernova 2019ehk. The orange represents the calcium-rich material created in the explosion. Purple reveals gas shed by the star right before the explosion.
Hide Caption
24 of 57
Photos: Wonders of the universe
The blue dot at the center of this image marks the approximate location of a supernova event which occurred 140 million light-years from Earth, where a white dwarf exploded and created an ultraviolet flash. It was located close to tail of the Draco constellation.
Hide Caption
25 of 57
Photos: Wonders of the universe
This radar image captured by NASA's Magellan mission to Venus in 1991 shows a corona, a large circular structure 120 miles in diameter, named Aine Corona.
Hide Caption
26 of 57
Photos: Wonders of the universe
When a star's mass is ejected during a supernova, it expands quickly. Eventually, it will slow and form a hot bubble of glowing gas. A white dwarf will emerge from this gas bubble and move across the galaxy.
Hide Caption
27 of 57
Photos: Wonders of the universe
The afterglow of short gamma ray burst that was detected 10 billion light-years away is shown here in a circle. This image was taken by the Gemini-North telescope.
Hide Caption
28 of 57
Photos: Wonders of the universe
This Hubble Space Telescope image shows NGC 7513, a barred spiral galaxy 60 million light-years away. Due to the expansion of the universe, the galaxy appears to be moving away from the Milky Way at an accelerate rate.
Hide Caption
29 of 57
Photos: Wonders of the universe
This artist's concept illustration shows what the luminous blue variable star in the Kinman Dwarf galaxy may have looked like before it mysteriously disappeared.
Hide Caption
30 of 57
Photos: Wonders of the universe
This is an artist's illustration of a supermassive black hole and its surrounding disk of gas. Inside this disk are two smaller black holes orbiting one another. Researchers identified a flare of light suspected to have come from one such binary pair soon after they merged into a larger black hole.
Hide Caption
31 of 57
Photos: Wonders of the universe
This image, taken from a video, shows what happens as two objects of different masses merge together and create gravitational waves.
Hide Caption
32 of 57
Photos: Wonders of the universe
This is an artist's impression showing the detection of a repeating fast radio burst seen in blue, which is in orbit with an astrophysical object seen in pink.
Hide Caption
33 of 57
Photos: Wonders of the universe
Fast radio bursts, which make a splash by leaving their host galaxy in a bright burst of radio waves, helped detect "missing matter" in the universe.
Hide Caption
34 of 57
Photos: Wonders of the universe
A new type of explosion was found in a tiny galaxy 500 million light-years away from Earth. This type of explosion is referred to as a fast blue optical transient.
Hide Caption
35 of 57
Photos: Wonders of the universe
Astronomers have discovered a rare type of galaxy described as a "cosmic ring of fire." This artist's illustration shows the galaxy as it existed 11 billion years ago.
Hide Caption
36 of 57
Photos: Wonders of the universe
This is an artist's impression of the Wolfe Disk, a massive rotating disk galaxy in the early universe.
Hide Caption
37 of 57
Photos: Wonders of the universe
A bright yellow "twist" near the center of this image shows where a planet may be forming around the AB Aurigae star. The image was captured by the European Southern Observatory's Very Large Telescope.
Hide Caption
38 of 57
Photos: Wonders of the universe
This artist's illustration shows the orbits of two stars and an invisible black hole 1,000 light-years from Earth. This system includes one star (small orbit seen in blue) orbiting a newly discovered black hole (orbit in red), as well as a third star in a wider orbit (also in blue).
Hide Caption
39 of 57
Photos: Wonders of the universe
This illustration shows a star's core, known as a white dwarf, pulled into orbit around a black hole. During each orbit, the black hole rips off more material from the star and pulls it into a glowing disk of material around the black hole. Before its encounter with the black hole, the star was a red giant in the last stages of stellar evolution.
Hide Caption
40 of 57
Photos: Wonders of the universe
This artist's illustration shows the collision of two 125-mile-wide icy, dusty bodies orbiting the bright star Fomalhaut, located 25 light-years away. The observation of the aftermath of this collision was once thought to be an exoplanet.
Hide Caption
41 of 57
Photos: Wonders of the universe
This is an artist's impression of the interstellar comet 2I/Borisov as it travels through our solar system. New observations detected carbon monixide in the cometary tail as the sun heated the comet.
Hide Caption
42 of 57
Photos: Wonders of the universe
This rosette pattern is the orbit of a star, called S2, around the supermassive black hole at the center of our Milky Way galaxy.
Hide Caption
43 of 57
Photos: Wonders of the universe
This is an artist's illustration of SN2016aps, which astronomers believe is the brightest supernova ever observed.
Hide Caption
44 of 57
Photos: Wonders of the universe
This is an artist's illustration of a brown dwarf, or a "failed star" object, and its magnetic field. The brown dwarf's atmosphere and magnetic field rotate at different speeds, which allowed astronomers to determine wind speed on the object.
Hide Caption
45 of 57
Photos: Wonders of the universe
This artist's illustration shows an intermediate-mass black hole tearing into a star.
Hide Caption
46 of 57
Photos: Wonders of the universe
This is an artist's impression of a large star known as HD74423 and its much smaller red dwarf companion in a binary star system. The large star appears to pulsate on one side only, and it's being distorted by the gravitational pull of its companion star into a teardrop shape.
Hide Caption
47 of 57
Photos: Wonders of the universe
This is an artist's impression of two white dwarfs in the process of merging. While astronomers expected that this might cause a supernova, they have found an instance of two white dwarf stars that survived merging.
Hide Caption
48 of 57
Photos: Wonders of the universe
A combination of space and ground-based telescopes have found evidence for the biggest explosion seen in the universe. The explosion was created by a black hole located in the Ophiuchus cluster's central galaxy, which has blasted out jets and carved a large cavity in the surrounding hot gas.
Hide Caption
49 of 57
Photos: Wonders of the universe
This new ALMA image shows the outcome of a stellar fight: a complex and stunning gas environment surrounding the binary star system HD101584.
Hide Caption
50 of 57
Photos: Wonders of the universe
NASA's Spitzer Space Telescope captured the Tarantula Nebula in two wavelengths of infrared light. The red represents hot gas, while the blue regions are interstellar dust.
Hide Caption
51 of 57
Photos: Wonders of the universe
A white dwarf, left, is pulling material off of a brown dwarf, right, about 3,000 light-years from Earth.
Hide Caption
52 of 57
Photos: Wonders of the universe
This image shows the orbits of the six G objects at the center of our galaxy, with the supermassive black hole indicated with a white cross. Stars, gas and dust are in the background.
Hide Caption
53 of 57
Photos: Wonders of the universe
After stars die, they expel their particles out into space, which form new stars in turn. In one case, stardust became embedded in a meteorite that fell to Earth. This illustration shows that stardust could flow from sources like the Egg Nebula to create the grains recovered from the meteorite, which landed in Australia.
Hide Caption
54 of 57
Photos: Wonders of the universe
The former North Star, Alpha Draconis or Thuban, is circled here in an image of the northern sky.
Hide Caption
55 of 57
Photos: Wonders of the universe
Galaxy UGC 2885, nicknamed the "Godzilla galaxy," may be the largest one in the local universe.
Hide Caption
56 of 57
Photos: Wonders of the universe
The host galaxy of a newly traced repeating fast radio burst acquired with the 8-meter Gemini-North telescope.
Hide Caption
57 of 57
In the case of the newly detected neutron star, dubbed J0740+6620, it's 333,000 times the mass of the Earth and 2.17 times the mass of the sun. But the star is only about 15 miles across. It's 4,600 light-years from Earth.
This is close to the limit of how much mass a compact object can contain before it crushes itself into a black hole.
The neutron star itself is rapidly spinning, which is called a pulsar because they send out beams of radio waves from each magnetic pole. The beams mimic the sweeping motion of a lighthouse beam, hence the name "pulsar."
Pulsars act like atomic clocks because they regularly pulse, so astronomers can use them to study space and time.
The star was detected by the Green Bank Telescope in West Virginia. Researchers published their findings about the star Monday in the journal Nature Astronomy.
The researchers weren't necessarily looking for this neutron star. Rather, it was happenstance as they searched for gravitational waves.
"At Green Bank, we're trying to detect gravitational waves from pulsars," said Maura McLaughlin, study author and Eberly Distinguished Professor of physics and astronomy at West Virginia University. "In order to do that, we need to observe lots of millisecond pulsars, which are rapidly rotating neutron stars. This is not a gravitational wave detection paper but one of many important results which have arisen from our observations."
They were able to measure its mass because of a white dwarf companion star that warped the space around both stars. This warping acted as a way to accelerate the pulsar's pulses through space. They could learn the mass of the white dwarf and neutron star this way through the "Shapiro Delay."
"Neutron stars are as mysterious as they are fascinating," said Thankful Cromartie, a graduate student at the University of Virginia and Grote Reber pre-doctoral fellow at the National Radio Astronomy Observatory in Charlottesville, Virginia. "These city-sized objects are essentially ginormous atomic nuclei. They are so massive that their interiors take on weird properties. Finding the maximum mass that physics and nature will allow can teach us a great deal about this otherwise inaccessible realm in astrophysics."
Due to their mysterious nature, astronomers still want to answer more questions about neutron stars and this unique one could help them. They want to know if crushed neutrons become a type of "superfluid," what the breakdown looks like and where the actual tipping point lies when gravity takes over.
"The orientation of this binary star system created a fantastic cosmic laboratory," said Scott Ransom, study co-author and an astronomer at the National Radio Astronomy Observatory. "Neutron stars have this tipping point where their interior densities get so extreme that the force of gravity overwhelms even the ability of neutrons to resist further collapse. Each 'most massive' neutron star we find brings us closer to identifying that tipping point and helping us to understand the physics of matter at these mind-boggling densities."
