Here鈥檚 a wish: 2018 will be the year when a whole load of apparent nothingness steals the show.
I鈥檓 talking about the monster black hole that lurks at the heart of the Milky Way. This year is shaping up to be its big moment, when we get to gawp at its raw beauty. While there is little to 鈥渟ee鈥� in the usual sense of that word, our galactic centre is home to a black hole more than four million times as massive as the sun. We know this because Sagittarius A* reveals itself by aggressively tugging on the orbits of nearby stars.
Its existence has been extrapolated from these kinds of indirect observations for many years, but hopes are high that the world鈥檚 most powerful telescopes will soon reveal this monster in the kind of detail that will make it a thing to behold even for those not versed in extreme astrophysics.
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Arguably the most likely project to grab the headlines is the (EHT), which is working right now to allow us to directly see Sagittarius A* for the first time. As black holes emit no light, this may seem surprising. However, EHT will take images of the hot, glowing gas that spirals around the black hole just before being swallowed by gravity so strong that not even light can escape it.
Planet-sized telescope
Seen from Earth, this glowing disc of gas is tiny. It is like trying to resolve a pebble on the moon, and so the EHT unites the observational power of up to 20 radio telescopes spread around the globe, linking them into a single telescope that is effectively the size of the planet.
The intense gravitational field near the black hole will bend and twist the light rays leaving this swirling disc. The result will be that EHT should see a very distorted view of this, realistically portrayed in the movie Interstellar when astronauts stare at the fictional black hole Gargantua. Recent Nobel prize recipient Kip Thorne, who was scientific adviser to the movie, ensured Gargantua possessed another key feature of such objects: an immense hole in the middle from which no light escapes. If EHT can see this , astronomers will be able to precisely measure the mass and spin of Sagittarius A*, directly testing Einstein鈥檚 ideas of gravity. Such an image would truly capture the public imagination.
As if that wasn鈥檛 enough, other astronomers are poised to use one of the stars that orbit this black hole to probe the very nature of space and time. For the last few decades, the paths of dozens of these stars have been accurately followed, tracing out the ellipses of their orbits. But in mid-2018, one of these, boringly named S0-2, will make its closest pass yet of the black hole, while travelling at a blistering 5000 kilometres a second.
Testing relativity
At such speeds and experiencing the immense gravitational pull of the black hole, the differences between Newton鈥檚 and Einstein鈥檚 laws of gravity will be at their most apparent. This will provide another direct test of the latter鈥檚 general relativity.
Two teams are chasing the prize of accurately measuring S0-2鈥檚 orbit through its closest approach. One is using the 10-metre Keck telescope in Hawaii with OSIRIS, an instrument that reveals the galactic centre in exquisite detail.
The other team is , an interferometer that combines the light from the four individual 8.2-metre mirrors of the Very Large Telescope in Chile to act as a single 100-metre telescope with superb resolution. Both groups are keenly focused on the galactic centre, because if they mess up these observations, they have more than 15 years to wait until SO-2鈥檚 next closest flyby.
Throughout this year, astronomers will be collecting data and crunching numbers, giving us the clearest view to date of Sagittarius A*, while testing Einstein鈥檚 physics by measuring the black hole鈥檚 intense gravitational pull.
The apparent nothingness at the centre of the galaxy is getting ready for its close-up, and 2018 is shaping up to be the year of the black hole.
Read more: When is a black hole not a black hole? When it鈥檚 a boson star
