Dust dims distant supernovae; two wavelengths let astronomers separate dust from distance

the gist

Type Ia supernovae are the standard candles of astronomy: they come from white dwarfs and reach a very consistent peak brightness, so how dim they appear reveals how far away they are. The catch is that dust between us and the explosion also dims the light. Astronomers solve this by photographing the same supernova in ultraviolet light, which dust blocks heavily, and in infrared light, which passes through almost untouched. The difference between the two reveals how much dust is in the way, so the true brightness can be recovered. Hubble can observe both wavelengths with the same instrument, which makes it ideal for this calibration. NGC 3810, the galaxy here, hosted a Type Ia supernova in 2022 and sits about 50 million light-years away.

how it works

A white dwarf that gains mass from a companion can reach a critical limit and detonate with a predictable peak luminosity. Dust scatters and absorbs blue and ultraviolet light much more than red and infrared, so comparing colours shows how much light was lost to dust rather than distance.

so what

This method underpins measurements of how fast the universe is expanding, because distances to remote galaxies rest on the supernova yardstick, and dust is one of the biggest sources of error.

the bigger pattern

Astronomers use a cosmic distance ladder, where each rung is calibrated by the one below. Cepheid variable stars, whose brightness is linked to their pulsation period, let Edwin Hubble show in the 1920s that galaxies lie far beyond the Milky Way, and supernovae extend that ladder to the most distant galaxies.

fun fact

Type Ia supernovae were central to the 1998 discovery that the expansion of the universe is accelerating.

ESA/Hubble · CC BY 4.0

Image: ESA/Hubble & NASA, D. Sand, R. J. Foley

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 ↗