A galaxy's spinning gas disc revealed the mass of its central black hole

the gist

NGC 4526 is a lenticular galaxy, a type that sits between spirals and ellipticals, and one of the brightest of its kind. It has a rapidly spinning disc of gas and stars at its centre that moves at more than 250 kilometres per second and reaches far out from the core. Measuring how fast that disc moves allowed astronomers to infer that the supermassive black hole at its centre has about 450 million times the Sun's mass. The method had not been used before to pin down a galaxy's central black hole. The galaxy is part of the Virgo cluster, and it has hosted two known supernovae, in 1969 and 1994.

how it works

Gas in the disc orbits the black hole, and its speed depends on how much mass is pulling at the centre. By measuring how fast the gas moves at different distances from the core, astronomers can calculate the mass inside, which is dominated by the black hole.

so what

Black holes are invisible, so their masses have to be inferred from how nearby matter moves. Using a spinning gas disc as a measuring tool gives astronomers a new way to weigh black holes in galaxies that are otherwise hard to study.

ESA/Hubble · CC BY 4.0

Image: ESA/Hubble & NASA Acknowledgement: Judy Schmidt

source: ESA/Hubble ↗

historyWikipediaclassic1336–1565 · Karnataka, India

Hampi was once one of the world's largest cities, until its Vijayanagara capital was destroyed in 1565

the gist

Hampi is a UNESCO World Heritage Site in Karnataka, India, with more than 1,600 surviving remains spread over 4,100 hectares. It was the capital of the Vijayanagara Empire from 1336 to 1565. Travellers from Persia and Portugal described it as a prosperous, wealthy and grand city with temples, markets and farms along the Tungabhadra River. By 1500 it was estimated to be the world's second-largest city after Beijing, and probably India's richest at the time. In 1565 a coalition of Muslim sultanates defeated the Vijayanagara Empire, its capital was conquered and destroyed, and the city was left in ruins. Hampi remains a religious centre, with the active Virupaksha Temple at its heart.

how it works

The city was built around a fortified core with temples, markets and water structures along the river, supplied by an extensive network of roads and waterworks. When the empire fell, the city was not rebuilt, so its stone monuments were left standing.

so what

Hampi shows how quickly a great city can vanish after a military defeat, and how a ruined capital can remain sacred. Its ruins give historians a view of medieval South Asia that few other sites can match.

fun fact

The name Hampi comes from Pampa, an old name for the Tungabhadra River.

From Wikipedia, the free encyclopedia · text CC BY-SA 4.0

Image: Wikimedia Commons

source: Wikipedia ↗

2 min

politicsshortCNA2:01

False allegations about Singapore’s hand in Indonesia’s markets and a made-up meeting

from CNA

CNA Verify has found close to 400 posts pushing falsehoods tying Singapore to Indonesia’s stock market rout and to a secret meeting that never took place. Together, they drew nearly 12 million views, and some were circulated by accounts that appeared to be working in concert, across multiple social media platforms.

Here’s how the disinformation campaign targeting Singapore was uncovered.

on YouTube: CNA ↗