Most of the space news we hear about comes out of the biggest ground-based telescopes and the observatories launched into space. I admit, I’m guilty of focusing on these sorts of news, too. The biggest and most expensive projects are often equipped to touch on a broader amount of science. (Hubble, for example, has cost billions but astronomers have used it consistently for 25 years to study everything from the atmospheres of planets orbiting other stars to the oldest and most-distant galaxies we can see in our universe. The Cassini spacecraft has spent over a decade at Saturn to uncover a diverse and exciting system — including learning that a saturnian moon that might have the right conditions for life.) But astronomers have a much larger bag of tools. One of those is an array of small telescopes working in unison. I’ve touched on one small-telescope setup before for Discover. Another is sounding rockets, with cameras and other detectors launched into Earth’s atmosphere to collect data for a few minutes. And yet another is balloons carrying instruments for weeks at a time. In this post, I want to bring attention to this third one.
Climb into the atmosphere
The type of light humans see — so-called visible light — makes up only a tiny portion of all types of radiation. Visible light passes right through Earth’s atmosphere, but most other radiation doesn’t. The atmosphere blocks some lower-energy light than what we can see, like infrared, and nearly all of the higher-energy radiation, like X-rays and gamma rays. Balloons are a great way to get your science experiment above at least part of Earth’s atmosphere, so that you have a better chance of catching some of that cosmic radiation.
Some balloons can stay afloat for hours, while others remain in the atmosphere for up to 100 days. It all depends on the balloon’s structure. Those with openings at the sides and bottom allow gas to escape as the balloon rises, and so they last for shorter amounts of time and ride the weather pattern. Those with the gas locked in can stay afloat for weeks. (And NASA is currently developing an Ultra Long Duration Balloon, or ULDB, that can fly for about 100 days.)
None of these balloons are what you’d find at your local Party City. Instead, most are enormous — like, 40 million cubic feet enormous. (NASA uses the following comparison: a football stadium could fit inside one of these balloons when it’s inflated. Because in America we like sports comparisons.) These balloons need to hold a huge volume of gas in order to lift thousands of pounds of scientific instruments and their electronic brains miles into the atmosphere. Even the smaller scientific balloons are still about a million cubic feet.
OK that’s all interesting, but the main question is: have science instruments flying via balloons collected important data? Yes.
We know of the telescopes that flew in space to study the universe’s earliest light, called the cosmic microwave background (CMB). And we know of ground-based observatories that also collect this light (like the BICEP2 hoopla from 2014). But some of the most important measurements of the CMB’s tiny variations in temperature were made in 1998 by a balloon flying for 10.5 days, and again in 2003, above Antarctica. That was the BOOMERANG project.
Another balloon-flown experiment above Antarctica discovered that the highest-energy particles from space, called ultra-high-energy cosmic rays, can generate pulses of radio light as those particles traverse Earth’s atmosphere. The ANITA project while it was lofted above Antarctica and hanging from a balloon, had detected those radio waves reflecting off the Antarctic ice.
And over the past several days, smaller balloons carrying lower loads — these are “only” 90 feet across and carry about 40 pounds of instruments — have been taking off from Northern Sweden for short flights. This is the BARREL project, and the onboard detectors are collecting X-rays to study Earth’s radiation belts.
I could talk about dozens more experiments that have flown into Earth’s atmosphere via balloons over the past few decades — but I’ll spare you the details for now. The point is that when you’re hearing about astronomical discoveries and news, know that it’s not coming from only billion dollar telescopes in space and multi-million dollar observatories on the ground. Smaller projects — and many of them built almost entirely by students — are also extremely important tools that we’re using to learn about the universe.
Earlier this year, the X-ray astronomy community experienced the highs of a successful observatory launch followed only a month later with the lows of that spacecraft’s demise. This was the Japanese-led Hitomi X-ray space telescope, and it was supposed to shed light on the high-energy processes of the universe. Instead, it broke apart shortly after giving astronomers a taste of what the craft could do. Its loss is a major hit to X-ray astronomers, but if the current talks pan out, we might see Hitomi version 2.0 launch in 2020 or 2021.
A bit of history
Here’s a short reminder about what happened earlier this year. ASTRO-H launched smoothly February 17 into its circular orbit around Earth. (As with other missions from the Japanese Aerospace Exploration Agency [JAXA], the ASTRO-H observatory was renamed just after launch. Its new name became Hitomi.) Everything appeared stable until March 26, when JAXA couldn’t communicate with the craft. Something was wrong.
We now know that after Hitomi had reoriented to observe a new target, a software error combined with human error caused the craft to misunderstand its rotation, which sent it rotating out of control. Several pieces of the spacecraft snapped off, including the solar panels and the optics portion that extended out from the main body. Losing these pieces was detrimental. Without solar panels Hitomi can’t collect energy to power the observatory. After investigating the March 26 events, JAXA announced April 28 that there was no way to restore the mission.
Why it mattered
The first time I heard about ASTRO-H was actually pretty late in its development. It was at a high-energy astrophysics meeting in April 2013, when X-ray astronomers were excitingly planning their observing projects.
ASTRO-H’s main instrument, the Soft X-ray Spectrometer (SXS), would revolutionize our view of the high-energy sky. The SXS would detect individual packets of X-ray light, and directly measure the heat of each of those X-ray photons. Scientists would know, for example how intense different regions of a gas cloud is at each X-ray energy. From that data, astronomers could piece together the movement of the object — mapping gas clumps of different elements flying out from the site of a stellar explosion or the motions of colliding galaxy clusters.
Other telescopes — like NASA’s Chandra and Europe’s XMM-Newton — have X-ray spectrometers, but those work differently. They spread the light into a rainbow, and can get detailed information on only point sources (like a bright star or distant active galaxy). The SXS could get an array of detail from several areas within an object (studying, for example, the winds near the center of a large galaxy). Plus, the SXS would be some 30 times as sensitive as any other space X-ray spectrometer.
It was ASTRO-H’s bread and butter. And it was a type of observation that X-ray astronomers desperately wanted.
This year’s high-energy astrophysics meeting took place the first week of April and just days after Hitomi’s communication failure. Instead of an upbeat session showcasing the progress of the spacecraft, team member Andy Fabian of the University of Cambridge, updated the X-ray astronomy community about the situation. “This is extremely sad and distressing for the enormous team working on this,” he said. The air in the room was heavy, gloomy.
During its five functioning weeks, Hitomi gave astronomers a taste of what the SXS instrument could have delivered. The observatory watched the bright center of the Perseus cluster of galaxies, and the collected data, said Fabian during this same presentation, “are completely transformational.” (The Hitomi team published these observations in a recent Nature paper.)
Even though Hitomi is completely lost, neither JAXA nor NASA are giving up on the idea of a successor mission.
A July 14 presentation from the JAXA Space Science Institute Director Tsuneda Saku overviews a suggested mission. (Unfortunately, the presentation PDF is in Japanese, and thus I had to rely on Google translate and similar apps.) From what I can make out, this observatory’s focus would be the SXS instrument. The spacecraft’s body and design would mimic Hitomi’s, which would therefore speed up development and construction. The launch goal is 2020 — if the mission and its funding is approved. During a July 15 press conference, the Japanese Minister of Education, Culture, Sports, Science and Technology Hiroshi Hase spoke of his support for a successor to Hitomi.
But even if JAXA does get approval to build Hitomi version 2.0, they need NASA’s involvement. That’s because JAXA wasn’t responsible for the main instrument — America’s space agency was.
That’s where the NASA X-ray Science Interest Group comes in. On June 8, the group of about 75 researchers discussed whether NASA might participate in a subsequent flight. In the weeks since, the group compiled a white paper to support the science case, and that was presented at a NASA Advisory Council Astrophysics Subcommittee meeting over the past two days. The science case is there — no one doubts that.
There is no X-ray instrument like the SXS in space right now. The European-led mission scheduled for a 2028 launch, Athena, will carry a similar instrument, but that’s a long time to wait for the views that X-rays astronomers had hoped to have now. If NASA and JAXA decide to move forward on a Hitomi successor with the SXS, the project could launch in 4 to 5 years. Both agencies will meet early next month to talk further about collaborating on a possible re-fly.
No scientist ever wants his or her experiment to go wrong. I’ve seen the disappointment before, for different astronomical projects; it’s heartbreaking. “There’s no question we went through the five stages of grief when we first heard about the spacecraft,” says NASA X-ray Science Interest Group Chair Mark Bautz.
Astronomers spend years, sometimes a lot longer, developing the hardware and the software to run said hardware, plus the subsequent observing plan. “We’ve been waiting for this for decades — literally,” says Harvard X-ray astronomer Randall Smith, “and to get a small taste and then lose it has just been awful.”
In space science, you usually get one shot. Maybe ASTRO-H will get a second.
We all have our favorites. Some stargazers prefer our rust-hued neighbor, Mars. Others instead look toward the Orion Nebula, the glowing stellar nursery. Personally, I’m quite fond of our galaxy’s center. There, the extremes of nature meet in spectacular fashion — and give us a pretty great laboratory to explore those extremes.
I know, other writers at Discover have also focused on this same target. There are reasons for that popularity.
First of all, a black hole takes center stage, and black holes are pretty rad. This one weighs in at 4 million times our sun, and all that mass is crammed into a space not even 20 times as wide as our sun. That makes for a very dense region of space. (Which certainly makes sense, because black holes are the densest objects nature makes.) Anything that comes too close to a black hole — anything that reaches beyond the point of no return — falls into the black hole’s gravitational pull. For our galaxy’s central supermassive black hole, with the unexciting name of Sagittarius A*, that tipping point is around 7.3 million miles. That sounds like a lot, but in the grand scheme of things, it’s not. Our sun’s radius is about 430,000 kilometers.
Whizzing nearby and around the black hole are dozens of stars. Tracking how those pinpricks of light move in the presence of Sagittarius A*’s immense gravitational pull is actually why astronomers even know the black hole exists and how heavy it is. But the black hole doesn’t just calmly sit at our galaxy’s center. It spins, likely dragging the fabric of space with it. The black hole munches on gas that comes too close. It throws out flashes of light. Surrounding the black hole is a tumultuous environment, laced with magnetic fields and hot plasma and who knows what else. It’s a constantly evolving, congested place.
Astronomers have trained a brigade of telescopes on the center of our galaxy. They’ve seen X-ray flashes and a diffuse X-ray glow. They’ve detected infrared flares, gamma-ray signals, and constant radio waves. The galactic center glows in every color of the radiation rainbow.
But there’s a lot they still haven’t seen, like the outline of that black hole — a shadow marking the border of no return, beyond which everything falls into Sagittarius A*’s gravitational pull. Astronomers probably won’t have to wait much longer to see it. They’ve been prepping a system of radio telescopes scattered across Earth to image that shadow, and the long-awaited photo may come next year.
We also think the black hole’s environs boost electrons and other lightweight particles to extraordinarily high energies. The power required to do this is out of reach of anything that exists on Earth, and so the center of our galaxy is the nearest laboratory to us to find out how particles with those energies can even exist.
The Milky Way’s center is a location rich in astronomy and physics and the extremes, making it a prime target for the armada of telescopes we have today. My declaration of the best place in the universe (well, aside from the comfort of our hospitable planet) makes for my introduction to the blogging world. Welcome to Astrobeat, where I’ll explore the ever-evolving rhythm of the universe — from new research, to the stories of those looking toward the cosmos, to historical perspectives, and everything in between.