What is Sagittarius A* (Sgr A*)?

The brightest star visible from Earth in the direction of the galactic center A supermassive black hole at the center of the Milky Way with a mass of about 4 million times that of the Sun A dense cluster of neutron stars at the galactic center A powerful radio pulsar orbiting the galactic center every 4 seconds

Why can we not observe the galactic center using visible-light telescopes?

The galactic center is too far away for any telescope to resolve individual objects there The intense gravity near Sgr A* bends visible light back before it can escape Dust and gas in the Milky Way's disk absorb visible light before it can travel the 26,000 light-years to us from the galactic center The galactic center spins so fast that its light is redshifted out of the visible range

What are the S-stars, and why are they important?

The oldest stars in the Milky Way, found in the stellar halo surrounding the galaxy Stars orbiting very close to Sgr A* whose tracked paths proved the existence of a supermassive black hole at the galactic center A type of variable star used as a distance indicator, similar to Cepheids Newly forming stars triggered by the radio jet from Sgr A*

What is the orbital period of star S2 around Sgr A*?

About 1 year — the same as Earth's orbit around the Sun About 16 years — far shorter than any planet orbits the Sun About 225 million years — one galactic year About 10,000 years — still fast compared to most stellar orbits

What was the maximum speed of star S2 as it swung past Sgr A* at closest approach?

About 30 km/s — the typical orbital speed of a star in the Milky Way disk About 300,000 km/s — exactly the speed of light About 7,650 km/s — roughly 2.5% of the speed of light About 1 km/s — moving very slowly due to the strong gravity holding it near

Who were awarded the 2020 Nobel Prize in Physics for their work on Sgr A*?

Kip Thorne and Rainer Weiss, for building the gravitational wave detector LIGO Andrea Ghez and Reinhard Genzel, for tracking S-stars and proving the supermassive black hole at the galactic center Jocelyn Bell Burnell and Antony Hewish, for discovering pulsars near the galactic center Stephen Hawking and Roger Penrose, for calculating the properties of Sgr A* from theory alone

When was the first direct image of Sgr A* released, and who produced it?

April 2019, by the same observation campaign that produced the M87 black hole image January 2015, by the LIGO collaboration as part of gravitational wave research May 2022, by the Event Horizon Telescope collaboration using a global network of radio observatories June 2030, by the James Webb Space Telescope in infrared light

Why was imaging Sgr A* harder than imaging the M87 black hole, even though Sgr A* is closer?

Sgr A* is actually farther away than M87*, making it harder to resolve fine detail Sgr A* is much smaller and its accretion features vary on timescales of minutes, making the image shimmer — and galactic dust scatters radio waves along the line of sight The Event Horizon Telescope could not be pointed at the galactic center from its location Sgr A* is currently dormant and emits no radiation for telescopes to detect

What complex structures exist near the galactic center beyond just the black hole itself?

The galactic center is completely empty except for Sgr A* itself Only a thin disk of gas circles the black hole — no stars survive that close Dense star clusters, complex magnetic fields, filaments of hot gas, and molecular clouds surround Sgr A* A ring of neutron stars captured from supernova explosions surrounds Sgr A*

How does Sgr A* compare in mass to the supermassive black hole in galaxy M87?

They are the same mass — all supermassive black holes have the same mass Sgr A* is larger — it is the most massive black hole known Sgr A* is about 4 million solar masses, while M87*'s black hole is about 6.5 billion solar masses — roughly 1,500 times more massive M87*'s black hole is smaller because it has been slowly evaporating via Hawking radiation