Comet Ison has made its closest approach to the Sun, passing about 1.2 million km above the star's surface.
Comet Ison seems to have been destroyed in its encounter with the Sun.
Astronomers continue to examine the great ball of ice and dust, to see how it is coping with the encounter.
Telescopes saw the giant ball of ice and dust disappear behind the star, but then fail to emerge as expected.
If Ison survives the immense heat and tidal forces and stays intact, it could brighten into a spectacular feature in the night sky.
Astronomers continue to search for the object, but it is almost certain the much vaunted "Comet of the Century" has gone out with a whimper.
An armada of special Sun-observing telescopes in space and on the ground are following Ison's progress.
Despite its great size, Ison was probably torn apart in the immense heat and tidal forces so close to the Sun.
Astronomers are hopeful the comet will pull though, but are realistic about the chances.
Professor Tim O'Brien, associate director of Jodrell Bank, UK, said: "The nucleus has gone very faint, which you wouldn't expect.
Prof Tim O'Brien, associate director of the UK's Jodrell Bank Observatory, said: "It's like throwing a snowball into fire. It's going to be tough for it to survive.
"We can't be sure - but it's not looking good. We'll have to keep watching."
"But luckily, it's a big object and it moves fast, so it won't spend too much time close to the Sun. There is a lot of uncertainty."
Comet Ison came from the Oort Cloud, a mysterious, icy region at the furthest reaches of our Solar System.
It has been hurtling towards the Sun, travelling at more than a million kilometres an hour. If it pulls through, what remains of the comet will head back out to the Oort Cloud, and beyond.
Its orbital trajectory suggests this will be the one and only time the inner Solar System sees Comet Ison.
Before the encounter, astronomers estimated Ison's nucleus to be several kilometres in diameter, which would have helped it to withstand the solar assault - at closest approach, it experienced temperatures up to about 2,000C, and would have been squeezed by Sun's enormous gravitational field.
If the comet does remain largely intact, scientists say the energy of our star should excite the dust and gas in Ison's core, allowing it to blaze a trail across the heavens.
