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A neutron star is what remains after a massive star roughly 8 to 20 times the mass of our Sun exhausts its nuclear fuel and collapses in a violent explosion called a supernova.
The result is an incredibly dense object: a sphere roughly 20 kilometers in diameter that packs more mass than the Sun. To put that in perspective, a teaspoon of neutron star material would weigh about a billion tons on Earth.
At such densities, protons and electrons merge to form neutrons hence the name. Neutron stars represent one of the most extreme environments in the known universe, where the laws of physics are pushed to their limits.
A pulsar is a rotating neutron star that emits beams of electromagnetic radiation usually radio waves from its magnetic poles. Because the star spins and the beam sweeps through space like a lighthouse, we detect it as regular pulses of radiation.
Some pulsars rotate hundreds of times per second with such precision that they rival atomic clocks in accuracy. The first pulsar was discovered in 1967 by Jocelyn Bell Burnell, and today we know of over 4,500 of them, most catalogued by the ATNF Pulsar Catalogue.
A magnetar is a rare type of neutron star with an extraordinarily powerful magnetic field roughly a thousand times stronger than that of an ordinary pulsar, and about a quadrillion times stronger than Earth's magnetic field.
These extreme fields power violent X-ray and gamma-ray bursts. A magnetar located within about 10 light-years of Earth would strip away our atmosphere. Fortunately, the closest known magnetar is thousands of light-years away.
Only about 30 magnetars are confirmed or suspected in the Milky Way and nearby galaxies. They are catalogued by the McGill Magnetar Catalogue.
A blitzar is a theoretical object proposed to explain fast radio bursts (FRBs), extremely brief but enormously powerful bursts of radio waves lasting only milliseconds that originate from billions of light-years away.
The leading hypothesis is that a blitzar begins as a massive, rapidly spinning neutron star that is temporarily held up against gravitational collapse by its own rotation. As the star gradually loses rotational energy through electromagnetic emission, it slows down, and at a critical threshold, it can no longer support its own mass and collapses into a black hole in an instant.
Blitzars have not been directly confirmed, and other explanations for FRBs exist. They are not included in this visualizer because no confirmed blitzar has been observed. By definition, they vanish the moment they form. They represent one of the most dramatic endpoints a neutron star can reach, second only to a collision with another neutron star or black hole.
The Magnificent Seven (M7) is the informal name for a group of seven nearby, thermally-emitting isolated neutron stars discovered by the ROSAT X-ray satellite. Unlike pulsars, they are radio-quiet they don't emit detectable radio pulses.
They are among the closest neutron stars to Earth, lying within a few hundred parsecs, and they glow in X-rays simply because they are still cooling down from their violent birth. Their proximity makes them valuable laboratories for studying neutron star surface properties.
Central Compact Objects are neutron stars found at the centers of supernova remnants the expanding shells of gas left behind after a stellar explosion. They are young, X-ray-emitting, and unusually quiet: no detected radio pulses, no strong magnetic activity.
Their weak magnetic fields and thermal X-ray emission make them a distinct and poorly understood class of neutron star. Only about 10 confirmed CCOs are known, making them among the rarest objects in this catalog.
To place a neutron star in three-dimensional space, we need three pieces of information: its right ascension, declination, and distance. Many known neutron stars have not had their distances measured with sufficient precision.
This is especially common for pulsars in the ATNF catalogue, where distance estimates can be uncertain or absent, and for magnetar candidates in the McGill catalogue that lack confirmed optical or X-ray counterparts.
Each color represents a different class of neutron star:
■ Red Magnetar (McGill)
■ Orange Magnetar Candidate
■ Yellow-green Pulsar with 2006 magnetar-like outburst
■ Cyan Magnificent Seven isolated neutron star
■ Purple Central Compact Object (CCO)
■ Pink Neutron star in a high-mass X-ray binary (HMXB)
■ Green Neutron star in a low-mass X-ray binary (LMXB)
■ White Ultraluminous X-ray (ULX) pulsar
■ Gray-blue Candidate neutron star in SN 1987A
■ Gold The Sun (reference point)
An X-ray binary is a neutron star (or a black hole) orbiting a normal star close enough to pull gas from it. The gas heats up to millions of degrees as it falls onto the neutron star and shines brightly in X-rays.
In high-mass X-ray binaries the companion is a massive young star, often a fast-spinning Be star or a supergiant, and the neutron star usually shows up as an X-ray pulsar. In low-mass X-ray binaries the companion is a star lighter than the Sun; these neutron stars often produce thermonuclear X-ray bursts, and some spin hundreds of times per second. Millisecond radio pulsars are thought to be the descendants of these systems.
Only X-ray binaries with direct evidence of a neutron star are shown, such as X-ray pulsations, thermonuclear bursts or cyclotron lines. Systems that may host a black hole, or whose compact object is unknown, are left out.
The Small and Large Magellanic Clouds host many high-mass X-ray binaries, because both had bursts of star formation in the last few tens of millions of years. Their X-ray pulsars are shown in the visualizer inside each galaxy.
Ultraluminous X-ray sources (ULXs) shine brighter than a neutron star should be able to by the usual accretion limit, so for years they were thought to be black holes. In 2014 pulsations were found in M82 X-2, proving that some of them are neutron stars accreting matter at extreme rates.
Most known ULX pulsars are in other galaxies millions of light-years away, too far to place on the 3D map; they are listed in The Catalog. The two in the Small Magellanic Cloud (SMC X-3 and RX J0209.6-7427) do appear in the visualizer. The Milky Way's own ULX pulsar, Swift J0243.6+6124, is shown as a high-mass X-ray binary.
Most neutron stars cannot be observed with optical telescopes because they are extremely small and faint in visible light. However, the Magnificent Seven are notable exceptions several have been detected optically with the Hubble Space Telescope, though they are extremely faint.
For radio amateur astronomers, some bright pulsars particularly the Vela Pulsar and the Crab Pulsar can be detected with modest radio setups. The coordinates shown in this visualizer are precise enough to point a telescope at the correct location in the sky.
All objects are converted from equatorial coordinates (J2000 RA/Dec + distance in kpc) to Galactocentric Cartesian coordinates using Astropy's Galactocentric frame with default parameters.
The Galactocentric frame places the origin at the Galactic center. The Sun is located at approximately x = −8.122 kpc, y = 0, z = 0.0208 kpc using Astropy's built-in constants (galcen_distance = 8.122 kpc, z_sun = 20.8 pc).
In the Three.js scene, the coordinate axes are remapped as: Three.x = galactic.x, Three.y = galactic.z, Three.z = −galactic.y, to orient the galactic plane horizontally.
ATNF distances are primarily derived from the dispersion measure (DM) of pulsar radio signals combined with models of the Galactic free electron density most commonly the YMW16 or NE2001 models. A small fraction have parallax measurements from VLBI.
DM-based distances carry significant systematic uncertainties, often 20–30%, particularly in regions of complex interstellar structure. This visualizer uses the ATNF-provided DIST field without further correction.
For pulsars in the Magellanic Clouds, the dispersion measure cannot give a reliable distance, so ATNF assigns most of them the distance of their galaxy: 49.7 kpc in the LMC and 59.7 kpc in the SMC. The project keeps these ATNF values as published, so in the 3D view those pulsars sit on a thin curved surface at that distance rather than filling the depth of each galaxy. This is a limitation of the available distances, not of the galaxies themselves. The Magellanic Cloud X-ray pulsars from other catalogues, which come with no distance at all, are placed with a tilted-plane model of each galaxy instead (see Data Sources).
M7 distances are taken from the compilation in Table 1 of Motch et al. (2007), which lists them in parsecs; parallaxes are behind the values for RX J1856.5-3754 and RX J0720.4-3125. They are converted to kiloparsecs by dividing by 1000, which places all seven within about 400 pc of the Sun.
For RBS 1223 the midpoint of the reported 76 to 670 pc range was used, and for RX J1605.3+3249 and RX J0420.0-5022 the published upper limits. These distances carry substantial uncertainties and should be treated as approximate in the 3D visualization.
For ATNF pulsars, extragalactic objects (40–70 kpc) are clustered using DBSCAN (eps=5 kpc, min_samples=5) and the largest cluster is assigned to the LMC, the smallest to the SMC.
For McGill magnetars, only two extragalactic objects exist (SGR 0526-66 in the LMC, CXOU J010043.1-721134 in the SMC). These are classified by 3D angular separation from the LMC center (RA 05h23m35s, Dec −69°45′22″) and SMC center (RA 00h52m38s, Dec −72°49′43″) using Astropy's separation_3d().
For ATNF pulsars, RAJ_ERR and DECJ_ERR are the positional uncertainties in the last quoted digit of the coordinate, as provided by the ATNF catalogue. For McGill magnetars, these correspond to RA_Err and Decl_Err from the McGill table, in arcseconds.
M7 and CCO objects sourced from SIMBAD do not currently include coordinate uncertainties in this dataset.
The ATNF catalogue contains over 4,500 pulsars, but many lack measured distances. After applying dropna on DIST, RAJ, and DECJ, filtering out objects beyond 20 kpc or with |z| > 5 kpc, and removing the objects this project takes from other catalogs (the Magnificent Seven, magnetars and some CCOs, which ATNF also lists), 4,216 pulsars remain.
The other 328 objects come from the McGill magnetar catalogue, the Magnificent Seven, the confirmed CCO sample, the XRBcats catalogues of X-ray binaries, the catalogues of X-ray pulsars in the Small and Large Magellanic Clouds, and a few individual objects from the literature. The total of 4,544 objects represents all neutron stars in the combined catalog with sufficient astrometric information for 3D placement. Objects without a distance still appear in The Catalog table.