A galaxy's brightest X-ray source is a small black hole, not its giant core

the gist

NGC 5643 is a grand design spiral, with two clear winding arms, about 40 million light-years away in the constellation Lupus. Its active galactic nucleus, a supermassive black hole feeding on gas, is not its brightest X-ray source. Researchers using ESA's XMM-Newton found a brighter X-ray object on the outskirts, called NGC 5643 X-1. The evidence points to a black hole about 30 times the Sun's mass, locked in orbit with a companion star that feeds it gas, forming a superheated disc.

how it works

Gas falling toward a black hole collects into a flattened disc, and friction heats it to hundreds of thousands of degrees. At that temperature the gas shines most strongly in X-rays. A small black hole pulling gas from a companion star can therefore look brighter in X-rays than a giant one whose gas supply is sparse.

so what

Stellar-mass black holes can briefly outshine the giant black holes at galaxy centres in X-rays. This is a useful reminder that brightness depends on how fast a system feeds, not only on its size.

ESA/Hubble · CC BY 4.0

Image: ESA/Hubble & NASA, A. Riess, D. Thilker, D. De Martin (ESA/Hubble), M. Zamani (ESA/Hubble)

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 ↗