Aug 13, 2019

Axios Space

By Miriam Kramer
Miriam Kramer

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1 big thing: The Hubble Constant conflict

Illustration: Aïda Amer/Axios

Scientists can’t agree on the answer to a foundational question in physics — how fast the universe is expanding — and to some, the debate signifies that their understanding of the universe may be about to shift.

The big picture: Cosmologists have been debating the expansion rate of the universe — known as the Hubble Constant — for decades, but today’s controversy centers on two camps that disagree on just how fast our 13.8 billion-year-old universe is moving.

Why it matters: The Standard Model — which Dennis Overbye of the New York Times calls "a collection of theories describing all the physical forces except gravity" — still has its limitations. Cosmologists are looking for a way to "break" the model in order to figure out exactly what they're missing.

  • "We need something to break. We're desperate for something to break," astrophysicist Katie Mack told Axios in an interview.
  • New observations and analysis further refining the Hubble Constant could provide that big break they're looking for.

Where it stands: Cosmologists using data from the Planck telescope's map of the cosmic microwave background emitted during the early days of the universe place the Hubble Constant at about 67 kilometers per second per megaparsec.

  • That number, however, is at odds with a study published this spring that tracked distances to stars to measure the rate of expansion.
  • The study — conducted by a team led by Adam Riess, a Johns Hopkins professor who won a Nobel Prize in 2011 for his work involving the expansion of the universe — places the constant at about 74 kilometers per second per megaparsec; 9% faster than expected.
  • Other studies looking at the late universe also found numbers somewhat in line with the Riess study, ranging from about 73 to 75.

The catch: If both values are shown to be correct, then it would mean that the universe is expanding at a rate that defies our best predictions, effectively breaking the Standard Model.

  • “That is, you know, in a way, that's the most exciting possibility, that both sets of measurements are right, and we're doing the wrong thing when we say one should be equal to the other because we're leaving out some chapter in the story,” Riess tells Axios.

But, but, but: A recent study using red giant stars to gauge expansion puts the constant in between the late and early universe values, hinting that the true answer may lie somewhere in the middle.

  • "I don't want to get too excited about discoveries in new physics yet," Mack says.

The bottom line: It’s too early to say whether our understanding of the universe is about to undergo a seismic shift, but scientists are paying close attention to any new data that could deepen our understanding of it.

2. What's next for the Hubble Constant

Thousands of galaxies seen by the Hubble Space Telescope. Photo: NASA/ESA/STScI

The Hubble Constant controversy is inspiring scientists to find new and inventive methods for testing just how fast our universe is expanding.

What's next: Researchers are now looking to a variety of different kinds of stars and other observations to try to nail down what the Hubble Constant actually is.

  • Scientists hope to use gravitational waves — ripples in the fabric of space and time — sent out by neutron stars colliding to gauge the expansion rate as researchers find more evidence of those events.
  • Data from the European Space Agency's Gaia spacecraft will also be key in the coming years, allowing scientists to measure cosmic distances with greater accuracy.
  • Cosmologists are continuing to refine their understanding of dark energy and dark matter, which could shift goalposts on the Hubble Constant as well.

Yes, but: In the immediate future, scientists will continue to parse the early and late universe numbers with a fine-toothed comb in the hopes that perhaps some overlooked element will help bring the numbers closer together.

  • "So I think to me, it really means that the systematics, and all of this, still require an awful lot of work to see if we can finally eventually agree on some value that is likely to be in the middle somewhere," Clemson University astronomer Dieter Hartmann told Axios.

Read more: Cosmologists debate how fast the universe is expanding (Quanta)

3. Interstellar dust on Earth

The remnant of a supernova. Photo: NASA/CXC/F. Vogt et al./ESO/VLT/MUSE/STScI

Radioactive dust sent out by ancient supernovas has been found in Antarctica, according to a new study in the journal Physical Review Letters.

The big picture: Researchers behind the study suggest that our solar system is currently flying through a cloud of cosmic material thought to be shaped by supernovas.

  • Those stellar explosions may leave behind traces of the radioactive isotope iron-60, which the scientists found in Antarctic snow.
  • This study and future work could help explain more about our solar system’s past and its movements through the Milky Way, according to a synopsis published by the American Physical Society.

What they found: The team behind the study thinks that the iron-60 atoms found in the region were delivered to Earth in the last 20 years.

  • "I think Earth essentially picked it [the element] up during the movement through the cloud, not like a real injection as you would expect from a very near supernova," Dominik Koll, an author of the study, tells Axios by email.
  • The scientists had been concerned that the isotope might have been created by nuclear weapons, but the team ruled that out when the other concentrations of bomb-created isotopes didn't match what they found in Antarctica.

What's next: Koll and his colleagues are hoping to get a look at older Antarctic snow in order to compare concentrations of iron-60 in the past to those found today.

  • Older samples may reveal exactly when our solar system traveled into the supernova-enriched cloud it appears to find itself within now.
4. The national security space race

A Falcon Heavy rocket launch in June. Photo: SpaceX

Four companies — SpaceX, Blue Origin, United Launch Alliance (ULA) and Northrop Grumman — have submitted proposals to become 1 of 2 launch providers for the U.S. Air Force from 2022 to 2026.

Why it matters: Launching commercial and government payloads to orbit is a competitive business, and locking in billions of dollars in revenue from the Air Force would be a huge win for any of these companies.

  • In 2020, the Air Force plans to pick 2 companies that will likely split dozens of national security launches 60/40.

The intrigue: All 4 companies have submitted their bids to the Air Force, but the fight to get to this point has been a long one, and it's not over yet.

  • Blue Origin filed a protest with the Government Accountability Office on Monday, saying that the Air Force competition favors the companies that have already flown national security missions like SpaceX and ULA and harms competition.
  • SpaceX has sued the U.S. government, claiming that the company was unfairly denied a share of a multimillion dollar award that the other 3 companies received from the Air Force, potentially putting SpaceX at a disadvantage.
5. Out of this world reading list

Happy birthday, Curiosity. Photo: NASA/JPL-Caltech/MSSS

Astronomers spot flashes from our galaxy's black hole (Ryan F. Mandelbaum, Gizmodo)

Inside Rocket Lab's plan to reuse its rocket (Michael Sheetz, CNBC)

ESA confirms 2nd ExoMars parachute test failure (Jeff Foust, Space News)

Blue Origin protests Air Force launch competition (Axios)

Curiosity has been on Mars for 7 years (Axios)

6. Your weekly dose of awe: A cosmic seagull in flight

The Seagull Nebula. Photo: ESO/VPHAS+ team/N.J. Wright (Keele University)

The Seagull Nebula takes on a red hue in a new photo taken by the European Southern Observatory's VLT Survey Telescope.

  • Radiation from young stars in the nebula — located about 3,700 light-years away — make the clouds glow and shape them, the ESO said in a statement.
  • 'The main components of the Seagull are three large clouds of gas, the most distinctive being Sharpless 2-296, which forms the 'wings,'" the ESO said.
  • "Spanning about 100 light-years from one wingtip to the other, Sh2-296 displays glowing material and dark dust lanes weaving amid bright stars."

If you haven't spotted it yet, the seagull's head is the bulbous mass of gas and dust on the lower right, with its wings spreading out to the left.

Miriam Kramer

Thanks for spending time with me this week. If this email was forwarded to you, subscribe here, and don't let the Hubble Constant get you down. 🚀