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A massive star has mysteriously vanished, confusing astronomers

A gigantic star makes off during an eight-year gap in observations.

Image source: ESO/L. Calçada
  • The massive star in the Kinsman Dwarf Galaxy seems to have disappeared between 2011 and 2019.
  • It's likely that it erupted, but could it have collapsed into a black hole without a supernova?
  • Maybe it's still there, but much less luminous and/or covered by dust.

A "very massive star" in the Kinman Dwarf galaxy caught the attention of astronomers in the early years of the 2000s: It seemed to be reaching a late-ish chapter in its life story and offered a rare chance to observe the death of a large star in a region low in metallicity. However, by the time scientists had the chance to turn the European Southern Observatory's (ESO) Very Large Telescope (VLT) in Paranal, Chile back around to it in 2019 — it's not a slow-turner, just an in-demand device — it was utterly gone without a trace. But how?

The two leading theories about what happened are that either it's still there, still erupting its way through its death throes, with less luminosity and perhaps obscured by dust, or it just up and collapsed into a black hole without going through a supernova stage. "If true, this would be the first direct detection of such a monster star ending its life in this manner," says Andrew Allan of Trinity College Dublin, Ireland, leader of the observation team whose study is published in Monthly Notices of the Royal Astronomical Society.

So, em...

Between astronomers' last look in 2011 and 2019 is a large enough interval of time for something to happen. Not that 2001 (when it was first observed) or 2019 have much meaning, since we're always watching the past out there and the Kinman Dwarf Galaxy is 75 million light years away. We often think of cosmic events as slow-moving phenomena because so often their follow-on effects are massive and unfold to us over time. But things happen just as fast big as small. The number of things that happened in the first 10 millionth of a trillionth of a trillionth of a trillionth of a second after the Big Bang, for example, is insane.

In any event, the Kinsman Dwarf Galaxy, or PHL 293B, is far way, too far for astronomers to directly observe its stars. Their presence can be inferred from spectroscopic signatures — specifically, PHL 293B between 2001 and 2011 consistently featured strong signatures of hydrogen that indicated the presence of a massive "luminous blue variable" (LBV) star about 2.5 times more brilliant than our Sun. Astronomers suspect that some very large stars may spend their final years as LBVs.

Though LBVs are known to experience radical shifts in spectra and brightness, they reliably leave specific traces that help confirm their ongoing presence. In 2019 the hydrogen signatures, and such traces, were gone. Allan says, "It would be highly unusual for such a massive star to disappear without producing a bright supernova explosion."

The Kinsman Dwarf Galaxy, or PHL 293B, is one of the most metal-poor galaxies known. Explosive, massive, Wolf-Rayet stars are seldom seen in such environments — NASA refers to such stars as those that "live fast, die hard." Red supergiants are also rare to low Z environments. The now-missing star was looked to as a rare opportunity to observe a massive star's late stages in such an environment.

Celestial sleuthing

In August 2019, the team pointed the four eight-meter telescopes of ESO's ESPRESSO array simultaneously toward the LBV's former location: nothing. They also gave the VLT's X-shooter instrument a shot a few months later: also nothing.

Still pursuing the missing star, the scientists acquired access to older data for comparison to what they already felt they knew. "The ESO Science Archive Facility enabled us to find and use data of the same object obtained in 2002 and 2009," says Andrea Mehner, an ESO staff member who worked on the study. "The comparison of the 2002 high-resolution UVES spectra with our observations obtained in 2019 with ESO's newest high-resolution spectrograph ESPRESSO was especially revealing, from both an astronomical and an instrumentation point of view."

Examination of this data suggested that the LBV may have indeed been winding up to a grand final sometime after 2011.

Team member Jose Groh, also of Trinity College, says "We may have detected one of the most massive stars of the local Universe going gently into the night. Our discovery would not have been made without using the powerful ESO 8-meter telescopes, their unique instrumentation, and the prompt access to those capabilities following the recent agreement of Ireland to join ESO."

Combining the 2019 data with contemporaneous Hubble Space Telescope (HST) imagery leaves the authors of the reports with the sense that "the LBV was in an eruptive state at least between 2001 and 2011, which then ended, and may have been followed by a collapse into a massive BH without the production of an SN. This scenario is consistent with the available HST and ground-based photometry."

Or...

A star collapsing into a black hole without a supernova would be a rare event, and that argues against the idea. The paper also notes that we may simply have missed the star's supernova during the eight-year observation gap.

LBVs are known to be highly unstable, so the star dropping to a state of less luminosity or producing a dust cover would be much more in the realm of expected behavior.

Says the paper: "A combination of a slightly reduced luminosity and a thick dusty shell could result in the star being obscured. While the lack of variability between the 2009 and 2019 near-infrared continuum from our X-shooter spectra eliminates the possibility of formation of hot dust (⪆1500 K), mid-infrared observations are necessary to rule out a slowly expanding cooler dust shell."

The authors of the report are pretty confident the star experienced a dramatic eruption after 2011. Beyond that, though:

"Based on our observations and models, we suggest that PHL 293B hosted an LBV with an eruption that ended sometime after 2011. This could have been followed by
(1) a surviving star or
(2) a collapse of the LBV to a BH [black hole] without the production of a bright SN, but possibly with a weak transient."

3 scientists school flat Earthers on the evidence

Can this end flat-Earth theory once and for all?

  • Despite centuries of evidence proving otherwise, there are an alarming number of people around the world who genuinely believe that the earth is flat. Bill Nye The Science Guy, NASA astronomer Michelle Thaller, and Neil deGrasse Tyson strongly disagree.
  • From simple experiments like standing at a seashore or looking through a telescope at other planets, to reading about navigation or viewing photos of Earth taken from space, the scientists share several ways that flat Earthers can see the truth for themselves.
  • Tyson explains why this trend doesn't qualify as a scientific debate and why it is actually dangerous for people to believe and, even worse, pass on these objectively false ideas.

Experiment proves old theory of how aliens might use black holes for energy

Researchers create a device to test a 50-year-old physics theory from the famed Roger Penrose.

Credit: NASA/CXC/M.Weiss
  • Scientists prove a 50-year-old physics theory by Roger Penrose.
  • The theory explains how energy could be harvested from black holes by advanced aliens.
  • Researchers from the University of Glasgow twisted sound waves to show that the effect Penrose described is real.
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6 billion planets like Earth? Scientists make stunning estimate

Astronomers propose new estimate of Earth-like planets in the Milky Way galaxy.

Credit: NASA/Ames Research Center/W. Stenzel/D. Rutter
  • Astronomers make new analysis based on data from NASA's Kepler space telescope.
  • The researchers estimate there may be as many as six billion Earth-like planets in our galaxy alone.
  • The scientists looked for planets that would be able to host life.
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Experts predict there are 36 contactable alien civilizations. Seriously.

Astrophysicists calculate the likely number of civilization out there capable of communicating with us.

Image source: DanieleGay/Shutterstock/Big Think
  • Taking into account what we do know, and mixing in some assumptions about life on Earth, a team of scientists have made predictions about alien life.
  • Even if aliens are relatively close by, they and we would have to be around for over 6,000 years just to chat.
  • Our current technology will likely not allow us to communicate with anyone or thing.

"The Ultimate Answer to Life, The Universe and Everything is...42!" — supercomputer Deep Thought in Douglas Adams' "Hitchhiker's Guide to the Galaxy"

Thus began a grand experiment involving humans and pan-dimensional, hyperintelligent mice designed to figure out more exactly what the question was anyway. As if in tribute to Adams, a group of astronomers this week announced their answer to a Great Question, and it is 36. This time, though, we at least know what the question is: How many contactable alien civilizations are there in our galaxy? But 36?

"I think it is extremely important and exciting because for the first time we really have an estimate for this number of active intelligent, communicating civilizations that we potentially could contact and find out there is other life in the universe — something that has been a question for thousands of years and is still not answered."

So says astrophysicist Christopher Conselice of University of Nottingham. He's co-author of a report published in the Astrophysical Journal, and Nottingham and his colleagues are dead serious about the 36 likely Communicating Extra-Terrestrial Intelligent (CETI: pronounced "chetee") civilizations.

The Drake Equation

Image source: Google

The scientists' calculations are a response to the Drake equation. In 1961 astronomer Frank Drake proposed that having knowledge of seven factors would allow scientists to reasonably estimate the number of intelligent alien civilizations out there. The Drake equation is so named because it's a mathematical formula, shown above. The seven factors are:

N = number of civilizations with which humans could communicate

R * = mean rate of star formation

f = fraction of stars that have planets

ne = mean number of planets that could support life per star with planets

fl = fraction of life-supporting planets that develop life

fi = fraction of planets with life where life develops intelligence

fc = fraction of intelligent civilizations that develop communication

L = mean length of time that civilizations can communicate

Even today, a lot of these blanks remain unfillable with our current knowledge. "Drake equation estimates have ranged from zero to a few billion [civilizations]— it is more like a tool for thinking about questions rather than something that has actually been solved." So Conselice and his colleagues set out to refine the equation based on what we do know, the one environment we're certain supports life as we know it: Earth.

The Astrobiological Copernican Principle

Image source: Christoph Burgstedt/Shutterstock

The Astrobiological Copernican Principle is based on the notion that what worked here could work elsewhere. "Basically, we made the assumption that intelligent life would form on other [Earth-like] planets like it has on Earth," Conselice tells The Guardian, "so within a few billion years life would automatically form as a natural part of evolution."

On the other hand, the report concludes these planets would be more likely to be orbiting low-mass M dwarf stars than strong stars like our Sun, and these dwarves are less likely to be life-supporting over an extended period.

"[If intelligent life] in a scientific way, not just a random way or just a very unique way, then you would expect at least this many civilizations within our galaxy." Such alien life might be more like off-planet "Star Trek" guest stars than, say, squid. Conselice says, "We wouldn't be super-shocked by seeing them."

Of course, begins the report, "One of the oldest questions that humans have asked is whether our existence—as an advanced intelligent species—is unique."

Getting to 36

Image source: metamorworks/Shutterstock

The study authors operated on the assumption that a planet's life would have to take form between 4.5 billion and 5.5 billion years after the creation of its system's star, as it did here. We've only been producing radio waves to send out there for 100 years, so that's assumed to be about the minimum time a civilization would have to be in existence and broadcasting for us to detect them, but really much longer — it's not as if we crawled out from the primordial ooze with radios.

More realistically, the authors expect that a CETI population would have to exist for an average of 3,060 years to be detectable, which means that if life formed in both places at the same time, we'd both need to be in existence for 6,120 years (beyond that minimal 100 years) for a single "Hi, we're from Earth," "Hi, we're not" exchange to occur.

Reactions

The report is, understandably, mostly being met with a shrug, at least according to three experts who checked in with The Guardian. "[The new estimate] is an interesting result, but one which it will be impossible to test using current techniques," says Andrew Coates of the Mullard Space Science Laboratory at University College London, though he agrees that the report's assumptions were reasonable. Patricia Sanchez-Baracaldo of University of Bristol notes just how many things have to go right for life to happen as it has here, suggesting that this additional what-if that makes accurate estimates even more difficult. Oliver Shorttle of the University of Cambridge cited the significant unanswered questions we would need to know the answers to in order to really hazard an irrefutably plausible estimate of CETI civilizations.

But we do have one answer, at least: 36. Sorry, two. Let's not forget 42.

Update, or What Smart People Do for Fun: Steven Wooding of U.K.'s Institute of Physics sent us the link to an online alien civilization calculator that he and his friend, molecular physicist Dominik Czernia, cooked up. It works with both of the models mentioned in this article to deduce the likely number of contactable civilizations given a set of variables. Enjoy!

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