Nasa has released never-before-seen images of 2I/Borisov, only the second known object to have visited our solar system from elsewhere.

The image shows the comet in front of a distant spiral galaxy, which can be made out to the side. But the focus of the imags is the bright blue centre of the image, which was taken by the Hubble Space Telescope as it tracked the comet through space.

The picture shows the comet on its way through our solar system as it makes its way back into the interstellar space where it once flew.

2I/Borisov was first spotted in August by a Crimean amateur astronomer who would give it its name, and caused a flurry of excitement across the world. Scientists quickly determined that it was the second interstellar object known to have visited our solar system, after the famous 'Oumuamua, and the first comet.

Since then, scientists have been taking images of the comet as it moves nearer to the Earth and can be seen in better detail. The first observations from Hubble came in October, and the new images come from November and December, offering a better look at the size and other details of the visitor.

Nasa's groundbreaking decade of space exploration: In pictures Show all 10 1 /10 Nasa's groundbreaking decade of space exploration: In pictures Nasa's groundbreaking decade of space exploration: In pictures Mystic Mountain, a pillar of gas and dust standing at three-light-years tall, bursting with jets of gas from fledgling stars buried within, was captured by Nasa's Hubble Space Telescope in February 2010 Nasa/ESA/STScI Nasa's groundbreaking decade of space exploration: In pictures The first ever selfie taken on an alien planet, captured by Nasa's Curiosity Rover in the early days of its mission to explore Mars in 2012 Nasa/JPL-Caltech/MSSS Nasa's groundbreaking decade of space exploration: In pictures Death of a star: This image from Nasa's Chandra X-ray telescope shows the supernova of Tycho, a star in our Milky Way galaxy Nasa Nasa's groundbreaking decade of space exploration: In pictures Arrokoth, the most distant object ever explored, pictured here on 1 January 2019 by a camera on Nasa's New Horizons spaceraft at a distance of 4.1 billion miles from Earth Getty Nasa's groundbreaking decade of space exploration: In pictures An image of the Large Magellanic Cloud galaxy seen in infrared light by the Herschel Space Observatory in January 2012. Regions of space such as this are where new stars are born from a mixture of elements and cosmic dust Nasa Nasa's groundbreaking decade of space exploration: In pictures The first ever image of a black hole, captured by the Event Horizon telescope, as part of a global collaboration involving Nasa, and released on 10 April 2019. The image reveals the black hole at the centre of Messier 87, a massive galaxy in the nearby Virgo galaxy cluster. This black hole resides about 54 million light-years from Earth Getty Nasa's groundbreaking decade of space exploration: In pictures Pluto, as pictured by Nasa's New Horizons spacecraft as it flew over the dwarf planet for the first time ever in July 2015 Nasa/APL/SwRI Nasa's groundbreaking decade of space exploration: In pictures A coronal mass ejection as seen by the Chandra Observatory in 2019. This is the first time that Chandra has detected this phenomenon from a star other than the Sun Nasa Nasa's groundbreaking decade of space exploration: In pictures Dark, narrow, 100 meter-long streaks running downhill on the surface Mars were believed to be evidence of contemporary flowing water. It has since been suggested that they may instead be formed by flowing sand Nasa/JPL/University of Arizona Nasa's groundbreaking decade of space exploration: In pictures Morning Aurora: Nasa astronaut Scott Kelly captured this photograph of the green lights of the aurora from the International Space Station in October 2015 Nasa/Scott Kelly

When this image was taken, the object was 326 million kilometres from Earth. Scientists can now use it and other observations to learn more about the comet.

"Hubble gives us the best measure of the size of comet Borisov's nucleus, which is the really important part of the comet," said David Jewitt, a professor of planetary science and astronomy at the University of California Los Angeles, whose team has captured the best and sharpest images of this first interstellar comet.

"Surprisingly, our Hubble images show that its nucleus is more than 15 times smaller than earlier investigations suggested it might be. The radius is smaller than half a kilometre. This is important because knowing the size helps us to determine the total number, and mass, of such objects in the Solar System, and in the Milky Way. Borisov is the first known interstellar comet, and we would like to know how many others there are."