The Week in Space and Physics #8
Astronomy has a dirty secret: the stars are not always what we think they are. Cases of mistaken identity abound in the field, from supernova that are really galaxies to planets that turn out to be stars. Astronomers, indeed, are often better at saying what something is not, rather than what it is.
That, unfortunately, is the nature of astronomy. The observational evidence is weak, limited to handfuls of photons surviving the long voyage across the heavens. Repeated measurements are scattered, giving only a few glances at significant events. Astronomers must become detectives; scouring the clues to work out what happened.
Such was the case with HR 6819, an object that was once claimed as the closest black hole to Earth. Two years ago a team at the European Southern Observatory found a pair of stars orbiting in an apparently unstable way. The only way to explain the orbits, they thought, was if something invisible lay between them.
Whatever it was, it seemed to be big: at least four times heavier than the Sun. Since no light is coming from it, the astronomers concluded that it was probably a black hole. Several years of observations seemed to back them up – as did the earlier finding of another similar black hole.
Now, however, a more detailed look at the system has cast doubt on the presence of any kind of invisible object at all. Astronomers in Belgium used a network of four telescopes in Chile to look more carefully at the stars and black hole. They found only two stars, one of which is dying.
The dying star has slowly been losing its outer layers to its companion, a process that sometimes happens in such stellar pairs. By now only the core of the star seems to remain, thus making it look much brighter and younger than it really is. This fooled the astronomers who originally observed it into thinking the star was far heavier than it really was.
Once the Belgian team re-ran the numbers, they eliminated the need for any invisible mass. That killed the idea of a nearby black hole, but it has revealed a rare stage of the stellar lifecycle. Models have shown that orbiting stars can strip material from each other – and that ultimately such systems should end up in exactly this state. Never before, however, have they seen it through their telescopes.
Russia’s Scientific Isolation Grows
Lifshitz and Landau’s Course of Theoretical Physics is a classic of the subject: a series of ten volumes known to every physicist. The authors, Lev Landau and Evgeny Lifshitz, belonged to a golden age of science; a period in which the Soviets prioritised science, developed atom bombs and reached out into space.
The era was not, of course, without repression. Landau, who later won the Nobel Prize, spent a year in prison for speaking out against Stalin. Sakharov, another Nobel Prize winner and father of the hydrogen bomb, spent years in exile. Still, despite the hardships, Soviet scientists made important contributions to physics and engineering.
Russia’s post-Cold War government squandered much of this powerhouse. In the chaos of the collapsing Soviet Union, scientific spending fell drastically, driving skilled researchers aboard. Other nations – China, India, South Korea – raced ahead, outpacing the Russian scientific output.
Still, as of the start of this year, Russia was still involved in many big collaborations. Russia is a key partner of the International Space Station, works with CERN on particle physics and is a member of ITER, an experimental fusion reactor under construction in France. Now, however, those agreements are under threat.
Following Russia’s invasion of Ukraine, CERN announced that no new partnerships will be formed with Russian universities. Current collaborations – and the large number of Russian scientists working at the facility – will, for now, be maintained. Given the breakdown in travel between the West and Russia, though, some slowdown in research will surely follow.
Other organisations are resisting calls for Russia to be isolated. The International Astronomical Union refused to ban Russian astronomers and ITER has, so far at least, kept ties with Russia open. Some researchers are instead focusing on helping Ukraine: offering positions specifically for Ukrainian researchers in safe countries.
Perhaps the greatest irony, of course, is that Landau – a hero of Soviet science – was born in Azerbaijan and spent many years working at the Kharkiv Institute of Physics. That city is today under siege by Russian forces; the Institute of Physics, home to a nuclear reactor, has already come under attack. Russia would do well to remember how international collaboration drove past scientific success.
The SLS Prepares for Launch
After years of development, the new Space Launch System rocket is finally sitting on the launch pad. Atop the massive rocket sits the Orion capsule: the vehicle that should, if all goes to plan, carry American astronauts back to the Moon.
This, however, is only a test run. NASA plan to conduct a practice launch, simulating the real thing until a few seconds before take-off. The SLS will be fully fuelled with liquid oxygen and hydrogen for the rehearsal. Operators will go through the sequence of activities that take place in an actual launch.
The idea, in short, is to prove that the SLS – a machine both hugely expensive and complicated – is ready to fly. As in any test, problems are possible, perhaps even likely. That, after all, is the purpose of testing: to find issues before they matter. Engineers will surely be watching every dial carefully, monitoring every step of the process for flaws.
Once done, the rocket will then head back to the hanger for last minute work and preparations, before the first real launch takes place this summer. That mission, known as Artemis I, will see an unmanned Orion capsule sent hurtling towards the Moon. After completing a series of tests and orbiting the Moon a few times, Orion will return to Earth.
A False Dawn?
Back in 2018 a group of astronomers in Australia claimed to have picked up a signal from the birth of the first stars in the cosmos. Those stars are too faint and old to see directly, at least with the telescopes we have on Earth. The effects of those stars, however, may be visible: resulting in a slight shift in the way hydrogen behaved in the early universe.
It was this signal that the team in 2018 thought they had seen; finding a small change in the way radio waves travelled through space. Soon after, though, other researchers started to raise doubts about the signal. Some argued that the signal was far stronger than predicted by theory. Others doubted that the signal was strong enough to be seen at all.
Now a second experiment has failed to pick up any sign of the signal. That, then, makes it even more unlikely that astronomers had really seen traces of the earliest stars. Instead the 2018 signal could have come from instrument errors.