Space Sunday: more Einstein, plus space planes and Wow!

This illustration reveals how the gravity of a white dwarf star warps space and bends the light of a distant star behind it. Credit: NASA, ESA, and A. Feild (STScI)

In his general theory of relativity, Albert Einstein predicted that whenever light from a distant star passes by a closer object, gravity acts as a kind of magnifying lens, brightening and bending the distant starlight in an effect known as “gravitational microlensing”.  While such microlensing has been observed using the Sun, it has never been used against an individual star (although it has been used binary pairs of stars) – until now.

During a two-year period between October 2013 and October 2015, astronomers used the Hubble Space Telescope (HST) did just that, allowing them to measure the mass of a star in the process.

The star in question is a white dwarf called Stein 2051 B, roughly 18 light years from Earth and part of a binary system, paired with a red dwarf. Essentially, the team of astronomers used Hubble to observe the effect the white dwarf had on the light being received from a star 5,000 light years away. By measuring the amount of apparent light deflection, the team were not only able to further confirm Einstein’s theory of relativity – they were able to measure the mass of the white dwarf itself, even though the deflection was tiny – only 2 milliarcseconds from its actual position.

“This microlensing method is a very independent and direct way to determine the mass of a star,” Kailash Sahu, the lead researcher on the project, explained following the publication of his team’s findings on June 7th, 2017. “It’s like placing the star on a scale: the deflection is analogous to the movement of the needle on the scale.”

On top of this, the observations confirmed the theory that a white dwarf star’s size is determined by its mass, first postulated in 1935 by Subrahmanyan Chandrasekhar, the Indian-American astronomer. Thus, a single set of observations have further confirmed Einstein’s theory of space-time to be correct (and sits alongside the detection of gravitational waves – see my last Space Sunday update – and observations of rapidly spinning pulsars in doing so), and confirmed the defining limits for a white dwarf star and allowed astronomers effectively measure the mass of a star.

Space Plane News

The United States Air Force has confirmed that the next mission for its X37B automated space plane will utilise a SpaceX Falcon 9 launch vehicle to boost it into orbit in August 2017.  This will be the fifth launch of the X-37B, which is also known as the Orbital Test Vehicle, and the first time a United Launch Alliance Atlas V booster hasn’t been used. It also marks the highest-profile US national security launch SpaceX will have signed-up for.

There are actually two of the uncrewed X-37B vehicles operated by the USAF which have been flown on alternate missions. The second of these two craft returned to Earth in May 2017 after spending an astonishing 718 days in orbit, carrying a mixed classified and non-classified cargo. The August mission will likely use the first of the two vehicles in its third mission, and will feature the Air Force Research Laboratory (AFRL) Advanced Structurally Embedded Thermal Spreader (ASETS-11) to test experimental electronics and oscillating heat pipes in the long duration space environment.

The USAF’s X-37B Orbital Test Vehicle (OTV) on the runway at Kennedy Space Centre at the end of the programme’s fourth mission, May 7th, 2017. The uncrewed vehicle is being “safed” by a Boeing team in protective suits to guard against harmful fumes and gases given off by the vehicle. Credit: USAF

At the same time as the USAF announcement about the X-37B, the South China Morning Post reported China’s own space plane programme is making “significant progress”.

China has been investigating the potential of operating some form of space plane since the late 1980s. Those plans ultimately didn’t go anywhere, and rumours of a new Chinese space plane, capable of flying astronauts and / or cargo to low Earth orbit started circulating in 2016, thanks to a news broadcast on Chinese state television service CCTV. However, as the report used imagery clearly taken from the UK’s Skylon programme, there was some doubt as to the veracity of the report.

 

In “announcing” the new space plane in 2016, China State television used images of the UK’s Skylon programme. Credit: CCTV

Like Skylon, the new Chinese vehicle, which the South China Morning Post refers to as athe Casic (the initials of the China Aerospace Science and Industry Corporation, said to be building the vehicle), will be able to take-off horizontally and use a hybrid propulsion system capable of flying it through the atmosphere and into space, carrying a crew and / or cargo to low Earth orbit. At the end of a mission, the vehicle will return to Earth and land on a conventional runway, where it can be re-serviced pretty much like a conventional military aircraft.

The South China Morning Post indicates that the new vehicle has “finished almost all ground experiments and overcome key technical hurdles such as engine design and construction”. However, no dates on when the vehicle might be rolled-out or start flight tests have been given. Nor have any specifics or official images of the vehicle been released. All that has been said is the vehicle will have an “aerodynamic shape” for atmospheric flight, and be larger than Virgin Galactic’s SpaceShipTwo, the VSS Unity.

WOW! Signal Explained?

In 1977, the sound of extraterrestrials was heard by human ears for the first time – or so people at the time thought. The Wow! Signal was detected by astronomer Jerry Ehman using Ohio State University’s Big Ear radio telescope, part of The Ohio State University’s Search for Extraterrestrial Intelligence (SETI) project.

The detector, which was dismantled in 1998, could be used to detect radio signals coming from a region of space, and record them numerically on a print out. Those radio signals associated with natural phenomena would print as the lower end of the scale (e.g. 1 through 4). Stronger signals, including those possibly being intentionally broadcast would record at higher numbers (e.g. 5-9). Whilst pointing the detector at a group of stars called Chi Sagittarii in the constellation Sagittarius on August 15th, 1977, Ehman captured a 72 second burst of radio waves so intense, the computer had to shift from numbers to letters to indicate the signal strength, prompting Ehman to circle the strongest sequence in the printout and write “Wow!” next to it, thus giving the signal its name.

The famous Wow! signal, recorded by the Big Ear telescope on August 15th, 1977 – now explained. Credit: Big Ear Radio Observatory and NAAPO

Over the last 40 years, the signal – although it was only a continuous unmodulated wave signal with no encoded information – has been cited as evidence that we are not alone in the galaxy. The only problem is, despite numerous attempts to listen to Chi Sagittarii in the hope of picking up the signal again, it has never been repeated.

Now, however, astronomer Antonio Paris, of St Petersburg College, Florida, believes he has solved the mystery: the cause of the signal is a pair of comets. Known as 266P/Christensen and 335P/Gibbs. Both comets, although in slightly different orbits around the Sun to one another, have clouds of hydrogen gas millions of kilometres in diameter surrounding them.The famous Wow! signal was detected at 1420MHz – the radio frequency hydrogen naturally emits.

What’s more, Paris has trace the orbits of the two comets and found they were both in the portion of the sky Big Ear was scanning on August 15th, 1977 – although at the time, neither was known to astronomers, having only been discovered in 2006.  While other attempts to detect the signal had been tried, it is likely none of them coincided with the presence in the sky of either of the two comets.

To confirm his theory that the comets might be responsible for the signal, aris used 10-metre radio telescope to scan the same portion of the sky where the WoW! signal was heard when comet 266/P Christensen was transiting it between January 20th and January 28th, 2017. He detected a signal remarkably similar to that picked-up by Big Ear.

Even so, some remain sceptical of Paris’ findings, and he admits more data is required. He’s therefore hoping to repeat the experiment in January, 2018, when comet 335P/Gibbs is transiting the same region of space.

Mars: GCR Risks Potentially Greater Than Thought

One of the major risks on a crewed mission to Mars is that of radiation exposure. As I’ve previously noted, there are two types of radiation crews in deep space will encounter: solar radiation and galactic cosmic rays (GCRs).

Solar radiation, while worrying, can be fairly decently mitigated against in a number of ways. GCRs, however far nastier. They are high energy particles which unlike solar radiation particles are exceptionally hard to stop or block when in interplanetary space. Data gathered during the Mars Science Laboratory flight to Mars in 2012 suggest an unprotected astronaut would receive a daily GCR radiation dose of around 1.8 milliSieverts throughout the trips to / from Mars – the equivalent of taking a fully body CAT scan every 5 or 6 days for 6 or 8 months, which simply isn’t healthy.

Until now, it had been believed that the one “positive” with GCRs was that the damage they cause would be constrained only to those cells they directly strike. However a new study from medical researchers at the University of Nevada, Las Vegas, suggests the potential damage GCRs cause to cells they strike could be transmitted to surrounding cells, modifying them and dramatically increasing the risk of lung, colon, breast, liver, and stomach cancers occurring later in life.

NASA Langley is working on using “GCR-proof” BNNTs within structures such as habitat units, space vehicle elements – and even as a flexible lining in space suits. Credit: NASA

These findings not only bring forth the need for more work in developing “GCR proof” materials and technologies, such as hydrogenated boron nitride nanotubes (BNNTs), suitable for use in spacecraft fabrication and space suit design, but also for research into so-called non-targeted effects (NTEs) of radiation on cells – not just with regards to missions to Mars, but potentially for missions in and around of cislunar space.

 

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