Comet Ison has been severely battered in its encounter with the Sun and largely destroyed.
Comet Ison, or some part of it, may have survived its encounter with the Sun, say scientists.
Telescopes saw the giant ball of ice and dust disappear behind the star, but only a dull streamer re-emerge.
The giant ball of ice and dust was initially declared dead when it failed to re-emerge from behind the star with the expected brightness.
Astronomers continued to search for the object, but it eventually became clear that the much vaunted "Comet of the Century" had gone out with a whimper.
All that could be seen was a dull smudge in telescope images - its nucleus and tail assumed destroyed.
Despite its great size, Ison was probably torn apart in the immense heat and tidal forces so close to the Sun.
But recent pictures have indicated a brightening of what may be a small fragment of the comet.
The European Space Agency's experts on the Soho Sun-watching satellite called the death of the comet at about 21:30 GMT.
Astronomers admit to being surprised and delighted, but now caution that anything could happen in the coming hours and days.
"Our Soho scientists have confirmed, Comet Ison is gone," Esa's twitter feed announced.
This remnant of Ison could continue to brighten, or it could simply fizzle out altogether.
Ison had captivated skywatchers with its promise ever since it was discovered by Vitali Nevski and Artyom Novichonok in 2012.
Karl Banttam wrote on the Nasa Comet Ison Observing Campaign blog: "It does appear that a least some small fraction of Ison has remained in one piece and is actively releasing material.
A "fresh", 2km-wide object flung in towards the inner Solar System from its home far beyond the outer planet Neptune, it was hoped it might produce a brilliant tail that would arc across the night sky, perhaps for weeks.
"We have no idea how big this nucleus is, if there is indeed one. If there is a nucleus, it is still too soon to tell how long it will survive.
And, as it got closer and closer to the Sun, its ices did indeed begin to vaporise, releasing dust that shimmered in a distinctive trailing stream.
"If it does survive for more than a few days, it is too soon to tell if the comet will be visible in the night sky."
But from early on, it was clear Ison was unlikely to be spectacular; it was just not brightening in the way experienced comet watchers had anticipated.
The European Space Agency, too, which had been among the first organisations to call the death of Ison, has had to re-assess the situation. A small part of the nucleus may be intact, its experts say.
This led scientists to fear for its survival when it eventually grazed past the star at a distance of just 1.2 million km at 18:35 GMT on Thursday.
How much of the once 2km-wide hunk of dirty ice may have survived is impossible to say.
Soho followed Ison as it began its sweep around the back of the Sun, but then failed to pick up a coherent object at the time it was supposed to re-emerge. A streak in the imagery was interpreted as the last fizzling of debris.
Passing just 1.2 million km above the surface of the Sun would have severely disrupted Ison. Its ices would have vaporized rapidly in temperatures over 2,000C. And the immense gravity of the star would also have pulled and squeezed on the object as it tumbled end over end.
Other telescopes such as Nasa's Solar Dynamics Observatory could detect no clear sign of the comet's nucleus, either.
Whatever happens next, comets are going to be a big feature in the news over the next year.
Passing close to the Sun, Ison would have been subjected to temperatures over 2,000C. And the immense gravity of the star would also have pulled and squeezed on the object as it tumbled end over end.
In 11 months' time, Comet Siding Spring will breeze past Mars at a distance of little more than 100,000km. And then in November 2014, the European Space Agency's Rosetta mission will attempt to place a probe on the nucleus of Comet 67P/Churyumov-Gerasimenko.
All the evidence suggests Ison's nucleus was torn apart in the close pass, in the same way that Comet Lovejoy - a previous hopeful in 2011 - was disrupted.
Comets will stay in the news, however. Next year, in October, Comet Siding Spring will breeze past Mars at a distance of little more than 100,000km. And then in November, the European Space Agency's Rosetta mission will attempt to place a probe on the nucleus of Comet 67P/Churyumov-Gerasimenko.
