Sagittarius A* (Galactic Center Black Hole)
Coordinates, GRAVITY S2 stellar orbit distance (8,277 pc) & mass (4.297 × 10^6 M☉), EHT 51.8 μas shadow, and Galactic Center guide for Sgr A*.
Aliases: Sgr A*, Galactic Center Black Hole
Compact Objects: Black Holes, Pulsars & Quasars
Relativistic stellar remnants and accreting supermassive black holes where extreme gravitational fields, magnetic fields, and relativistic jets dominate.
Cataloged Profiles4 Objects
ClassificationBlack Holes, Pulsars & Quasars
Machine-Readable DataJSON Shard (compact-objects.json)
Physical & Observational Overview
Compact objects represent the end states of gravitational collapse: neutron stars pack ~1.4 M☉ inside a ~12 km radius supported by neutron degeneracy pressure and strong-force repulsion, whereas stellar and supermassive black holes collapse inside relativistic event horizons.
High-precision VLBI (Event Horizon Telescope), near-infrared adaptive optics (GRAVITY), and X-ray/radio timing pin down the masses and distances of these extreme objects with sub-percent to few-percent accuracy.
Classification Criteria: Categorized by compact mass scale and emission mechanism: rotation-powered neutron star pulsars (~1.4 M☉), stellar-mass X-ray binary black holes (~10–25 M☉), galactic center supermassive black holes (~10⁶–10¹⁰ M☉), and luminous quasars (AGN).
Visual Observing Regime: While event horizons and neutron star surfaces are microscopic, amateur observers can view the 8.9-magnitude O-supergiant companion of Cygnus X-1, the +12.85-magnitude optical point of quasar 3C 273 at 2.4 billion light-years, and the synchrotron nebula powered by the Crab Pulsar.
Companion Theoretical Reference: Explore general relativity, black hole horizons, and neutron star physics on FastCosmos.us.
Black Holes, Pulsars & Quasars Comparison Table
| Object | Constellation | Classification | RA (J2000) | Dec (J2000) | Min. Instrument | Best Season |
|---|---|---|---|---|---|---|
| Sagittarius A* (Galactic Center Black Hole) | Sagittarius | Supermassive black hole at the dynamical center of the Milky Way | 17h 45m 40.04s | -29° 00′ 28.1″ | Binoculars / wide-field telescope to view the surrounding Galactic Center star clouds | Summer (June–August) |
| Cygnus X-1 (HDE 226868 X-Ray Black Hole) | Cygnus | High-mass X-ray binary (stellar-mass black hole + O9.7 Iab blue supergiant) | 19h 58m 21.67s | +35° 12′ 05.8″ | 60 mm telescope (or 15×70 binoculars) to view the 8.95-mag companion HDE 226868 | Summer to Autumn (June–November) |
| Crab Pulsar (PSR B0531+21 Neutron Star) | Taurus | Young rotation-powered radio, optical, X-ray & gamma-ray pulsar (SN 1054 core) | 05h 34m 31.97s | +22° 00′ 52.2″ | 350–450 mm (14–18 inch) telescope under steady, dark skies at 250×+ | Late Autumn to Winter (November–March) |
| 3C 273 (Brightest Quasar in Virgo) | Virgo | Optically brightest quasar / blazar (radio-loud active galactic nucleus) | 12h 29m 06.70s | +02° 03′ 08.6″ | 150–200 mm (6–8 inch) telescope with a detailed finder chart | Spring (March–June) |
Detailed Black Holes, Pulsars & Quasars Profiles
Cygnus X-1 (HDE 226868 X-Ray Black Hole)
Coordinates, VLBA/Gaia distance (2.22 kpc), 21.2-M☉ stellar black hole mass, 5.60-day O-supergiant binary, and observing guide for Cygnus X-1.
Aliases: Cyg X-1, HDE 226868, V1357 Cygni, HIP 98298
Crab Pulsar (PSR B0531+21 Neutron Star)
Coordinates, 33.08 ms spin period, 16.5-mag optical flashes, spin-down luminosity, and high-aperture observing guide for the Crab Pulsar.
Aliases: PSR B0531+21, PSR J0534+2200, CM Tauri, NP 0532
3C 273 (Brightest Quasar in Virgo)
Coordinates, redshift z = 0.1583 (~2.4 billion ly), magnitude 12.85, supermassive black hole accretion, and observing guide for quasar 3C 273.
Aliases: PG 1226+023, HIP 60936
Related Astrometric & Optical Reference Guides
Proper Motion, Radial Velocity & Redshift
How astronomers combine tangential proper motion (mas/yr), Doppler radial velocity (km/s), and cosmological redshift (z) to reconstruct 3D space motion.
Angular Size, Separation & Field of View
How angular diameter (degrees, arcminutes, arcseconds), spherical angular separation, and small-angle physical diameter relate to telescope field of view.
Trigonometric Parallax, Parsecs & Gaia DR3
How trigonometric parallax (d_pc = 1 / p_arcsec), the distance modulus equation, Hipparcos, and Gaia DR3 microarcsecond astrometry measure cosmic distances.