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Beyond the Milky Way — a game-changing discovery

As I’ve noted elsewhere (Beyond the infinity of black holes), it wasn’t long ago — maybe a 100 years or so, that our view of the cosmos was much more circumscribed. Those who studied cosmology — physicists, astronomers, et al, viewed our cosmos in a much different way, at a much different scale — basically an island universe: Earth, the solar system and the Milky Way. We existed in a galaxy, but a singular one.

Now, almost one hundred years later, it is difficult to fully appreciate how much our picture of the universe has changed in the span of a single human lifetime. As far as the scientific community in 1917 was concerned, the universe was static and eternal, and consisted of a single galaxy, our Milky Way, surrounded by a vast, infinite, dark, and empty space. This is, after all, what you would guess by looking up at the night sky with your eyes, or with a small telescope, and at the time there was little reason to suspect otherwise. — Krauss, Lawrence. A Universe from Nothing: Why There Is Something Rather than Nothing (pp. 1-2). Atria Books. Kindle Edition.

The game-changing discovery was highlighted back in 2011 by this Space.com article “Star That Changed the Universe Shines in Hubble Photo” (May 23, 2011).

In homage to its namesake, the Hubble Space Telescope recently photographed a star that astronomer Edwin Hubble observed in 1923, changing the course of astronomy forever.

The star is a variable star that pulses brighter and dimmer in a regular pattern, which allowed scientists to determine its distance, suggesting for the first time that other galaxies exist beyond our own Milky Way.

“I would argue this is the single most important object in the history of cosmology,” said astronomer David Soderblom of the Space Telescope Science Institute in Baltimore, Md., who proposed pointing the Hubble Space Telescope at the star.

Can you say Cepheid variable?

When I get bogged down in the 10^-n scale of things, a reminder about standard candles at the other end of the scale of things helps restore my perspective on how science works — that, at its best, science moves us beyond circumscribed views.

 

17 thoughts on “Beyond the Milky Way — a game-changing discovery

  1. January 12, 2018, Space.com: “Whirlpool Galaxy: Exploding With Supernovas.”

    M51 was first catalogued by Charles Messier in 1773 while the astronomer was plotting objects in the sky that could confuse comet-hunters. “M51” is a reference to “Messier 51,” one of about 110 entries now plotted in his Catalogue of Nebulas and Star Clusters. …

    It would take about 70 years to learn more about the fuzzy object’s structure, however. It was first discerned by William Parsons, using a 72-inch reflector telescope in 1845. “His drawing of the spiral galaxy M51 is a classic work of mid-19th-century astronomy,” said Encyclopedia Britannica of Parsons’ observations.

    Parsons’ discovery was the first so-called “spiral nebula” ever discovered, and in the five years following he found 14 more of these objects, according to the STScI. It was unclear for decades if these objects were a part of the Milky Way Galaxy or things that were independent of that.

    It wasn’t until Edwin Hubble used Cepheid variable stars to chart cosmic distances in M31 (the Andromeda Galaxy) in the 1920s that astronomers understood they were actually distant galaxies.

  2. Regarding the scale of space and time beyond the Milky Way, this brief BBC News article “Hubble scores unique close-up view of distant galaxy“(January 16, 2018) notes the discovery of one of the oldest galaxies.

    Astronomers were lucky when the orbiting observatory captured the image of a galaxy that existed just 500 million years after the Big Bang.

    The image was stretched and amplified by the natural phenomenon of gravitational lensing, unlocking unprecedented detail.

    Such objects usually appear as tiny red spots to powerful telescopes.

    Distance and age are linked in astronomy; because of the time taken for light to traverse the vast expanse in-between, we see the galaxy as it was more than 13 billion years ago.

  3. More in science news on this topic, with this February 26th Space.com article “The Universe Is Expanding Faster Than We Thought, Hubble Data Suggests.” The article includes a video by astrophysicist Paul Sutter (a frequent contributor on Space.com) with some background on Cepheid variable stars and a summary chart “Three Steps to Measuring the Hubble Constant.”

    The article discusses the interplay of recent data from the Hubble Space Telescope and European Space Agency’s (ESA) Planck satellite with the Big Bang theory.

    Researchers analyzed 19 galaxies, including NGC 3972 (left) and NGC 1015 (right), which are 65 million and 118 million light-years from Earth, respectively. Both possessed pulsating stars called Cepheid variables that let researchers determine the distance to the galaxies.

    Researchers measured the universe’s expansion by calculating the distance to several very distant stars called Cepheid variables, which pulse regularly and let researchers determine the distance to them based on their brightness. The eight newly measured Cepheids are 10 times farther away than any studied previously. Then, the researchers compared the brightness of those stars to the brightness of supernovas in the same galaxies, and compare them with the brightness of supernovas that are even farther out.

  4. So, “How Many Galaxies Are There?” asks this March 19, 2018, Space.com article. “In our own cosmos … astronomers will be better able to refine the number upon the launch of the James Webb Space Telescope …”

    Whatever instrument is used, the method of estimating the number of galaxies is the same. You take the portion of sky imaged by the telescope (in this case, Hubble). Then — using the ratio of the sliver of sky to the entire universe — you can determine the number of galaxies in the universe.

    “This is assuming that there is no large cosmic variance, that the universe is homogenous,” Livio said. “We have good reasons to suspect that is the case. That is the cosmological principle.”

    “The simplest assumption to make is that if you viewed the contents of the universe with sufficiently poor vision, it would appear roughly the same everywhere and in every direction,” NASA stated. “That is, the matter in the universe is homogeneous and isotropic when averaged over very large scales. This is called the cosmological principle.”

    One example of the cosmological principle at work is the cosmic microwave background, radiation that is a remnant of the early stages of the universe after the Big Bang. Using instruments such as NASA’s Wilkinson Microwave Anisotropy Probe, astronomers have found the CMB is virtually identical wherever one looks.

  5. So, as previously noted, estimating cosmic distances relies on standard candles such as Cepheid variable stars. But so-called “yardsticks” based on measuring parallax are fundamental to establishing distances to those Cepheids. This April 5, 2018 Space.com article “Cosmic ‘Yardstick’ Measures Distance to One of Universe’s Oldest Objects” discusses refinements of that method.

    Astronomers are constantly searching for better ways to figure out how far away objects in the sky are. Recently, for the first time, scientists measured the distance to one of the oldest collections of stars in the universe with great precision, thanks to two years of data from the Hubble Space Telescope.

    The new method to determine distance from Earth could help scientists estimate the age of the universe, the researchers said in a statement from the Space Telescope Science Institute (STScI) in Baltimore.

  6. As noted above, ~100 years ago the cosmos was viewed as “static and eternal, and consisted of a single galaxy, our Milky Way.” Then there were other galaxies. Then the notion that the universe was expanding. This Space.com article (May 16, 2018) “How Anti-Religious Bias Prevented Scientists from Accepting the Big Bang” notes how this latter idea was even more revolutionary.

    … things didn’t always look so certain for the Big Bang. In its most nascent form, the idea was known as the hypothesis of the primeval atom, and it originated from an engineer turned soldier turned mathematician turned Catholic priest turned physicist by the name of Georges Lemaître. When Lemaître published his idea in the eminent journal Nature in 1931, a response to observational data suggesting that space was expanding, he ruffled a lot of feathers. As UC-San Diego professor of physics Brian Keating wrote in his recent book Losing the Nobel Prize, “Lemaître’s model… upset the millennia-old orthodoxy of an eternal, unchanging cosmos. It clearly implied that everything had been smaller and denser in the past, and that the universe must itself have had a birth at a finite time in the past.”

    … It also violated an accepted notion known as the perfect cosmological principle, which suggested that the Universe looks the same from any given point in space and time.

    For these reasons, English astronomer Sir Fred Hoyle gathered with a few colleagues to formulate the Steady State theory of the cosmos.

  7. And not even 100 years ago, the origin of elements was unclear, as this June 3, 2018, Space.com article “Elements From the Stars: Unexpected Discovery Upended Astrophysics 66 Years Ago” discusses. A celebration of a discovery by astronomer Paul Merrill.

    On May 2, 1952, Merrill reported his discovery in the journal Science. Among the three interpretations offered by Merrill was the answer: Stars create heavy elements! Not only had Merrill explained a puzzling observation, he had also opened the door to understand our cosmic origins. Not many discoveries in science completely change our view of the world – but this one did.

    In the early 1950s, it was still unclear how the elements that make up our universe, our solar system, even our human bodies, were created. Initially, the most popular scenario was that they were all made in the Big Bang.

    Merrill’s discovery marked the birth of a completely new field: stellar nucleosynthesis.

  8. Regarding the “cosmic distance ladder,” this Phys.org article recaps some recent research about the Hubble constant: “New Hubble measurements confirm universe is expanding faster than expected” by Johns Hopkins University (April 25, 2019).

    New measurements from NASA’s Hubble Space Telescope confirm that the Universe is expanding about 9% faster than expected based on its trajectory seen shortly after the big bang, astronomers say.

    The new measurements, published April 25 in the Astrophysical Journal Letters, reduce the chances that the disparity is an accident from 1 in 3,000 to only 1 in 100,000 and suggest that new physics may be needed to better understand the cosmos.

    As the team’s measurements have become more precise, their calculation of the Hubble constant has remained at odds with the expected value derived from observations of the early universe’s expansion by the European Space Agency’s Planck satellite based on conditions Planck observed 380,000 years after the Big Bang.

    The article includes two YouTube visualizations:

    Animation of cosmic distance ladder — HubbleESA (uploaded on Sep 14, 2016) — This animation shows the principle of the cosmic distance ladder used by Adam Riess and his team to reduce the uncertainty of the Hubble constant.

    Hubblecast 120 Light: Continued Discrepancy in the Universe’s Expansion Rate — HubbleESA (published on Apr 25, 2019 — Measurements of today’s expansion rate do not match the rate that was expected based on how the Universe appeared shortly after the Big Bang over 13 billion years ago. Using new data from the NASA/ESA Hubble Space Telescope, astronomers have significantly lowered the possibility that this discrepancy is a fluke.

  9. Re the scale of the universe and cosmic expansion, here’s another (Space.com) article on current research on the Hubble constant: “New Hubble Constant Measurement Stokes Mystery of Universe’s Expansion” (July 22,2019).

    this new study used red giant stars in nearby galaxies to measure the expansion rate. Red giants are nonvariable stars that all reach the same peak luminosity toward the end of their life cycle. Measuring the brightness of red giant stars at this stage of stellar evolution can help scientists figure out their distance, according to the statement.

    Freedman’s team chose this different approach to measuring the Hubble constant in hopes of figuring out why earlier measurements using other methods have been so inconsistent. “Our initial thought was that if there’s a problem to be resolved between the Cepheids and the cosmic microwave background, then the red giant method can be the tie-breaker,” Freedman said.

    “Naturally, questions arise as to whether the discrepancy is coming from some aspect that astronomers don’t yet understand about the stars we’re measuring, or whether our cosmological model of the universe is still incomplete,” Freedman [1] said. “Or maybe both need to be improved upon.”

    The study was accepted for publication in The Astrophysical Journal.

    [1] Wendy Freedman, a professor of cosmology at the University of Chicago and lead author of the new study.

  10. If you’re a fan of images from interplanetary space probes and space telescopes, then you might know that those color images are constructed from monochrome images taken by separate spectral filters. Like colorizing an old black & white film. This Fstoppers article “How Scientists Accurately Colorize Hubble Telescope Images of Space” (August 1, 2019) by Robert K Baggs contains a Vox YouTube video on the question, “So how do scientists know the correct colors to apply?”

    This video at the top of this article explains the complicated process of identifying wavelengths and the chemicals that make up what constitutes the image. Enjoy this captivating breakdown of how NASA approaches the colorization of Hubble black and white images, …

    Notes

    In order to understand the universe at deeper levels (whether on a microscopic or cosmic scale), we need to go beyond our natural vision and even the visible spectrum. Gathering and processing that data and extracting information on the invisible can involve many steps of careful visualization. False-color images may be beautiful, but their purpose is to address certain questions visually, not just take us on a sightseeing (eyeball) trip.

    Wiki > Hubble Space Telescope:

    All images from Hubble are monochromatic grayscale, taken through a variety of filters, each passing specific wavelengths of light, and incorporated in each camera. Color images are created by combining separate monochrome images taken through different filters. This process can also create false-color versions of images including infrared and ultraviolet channels, where infrared is typically rendered as a deep red and ultraviolet is rendered as a deep blue.

  11. Regarding the cosmic distance ladder and standard candles, here’s another article about refining distances to galaxies.

    • Phys.org > “Astronomers determine distances to 18 dwarf galaxies” by Tomasz Nowakowski (Oct 12, 2020)

    Astronomers from the Special Astrophysical Observatory (SAO) in Nizhnij Arkhyz, Russia, have conducted photometric observations of dwarf galaxies identified by the ALFALFA survey. The results allowed the researchers to determine accurate distances of 18 dwarf galaxies. The study is detailed in a paper published October 1 on the arXiv pre-print repository.

    One of the methods to obtain these distances is known as TRGB and is based on measuring the position of the tip of the red giant branch stars.

    SAO’s astronomers Olga Galazutdinova and Nikolay A. Tikhonov have used the TRGB technique to accurately determine distances of 18 dwarf galaxies. The dwarfs were detected by the Arecibo Legacy Fast ALFA (ALFALFA) survey, and their images were obtained by the Hubble Space Telescope (HST).

    Notes

    Wiki:

    ALFALFA = Arecibo Legacy Fast ALFA. ALFA is the abbreviation of Arecibo L-Band Feed Array.

    Tip of the red-giant branch

    When distant stars at the TRGB are measured in the I-band (in the infrared), their luminosity is somewhat insensitive to their composition of elements heavier than helium (metallicity) or their mass; they are a standard candle with an I-band absolute magnitude of –4.0±0.1. This makes the technique especially useful as a distance indicator. The TRGB indicator uses stars in the old stellar populations (Population II).

  12. What Hubble sees and not.

    • NASA > “Hubble Views a Galaxy with More than Meets the Eye” (Oct 1, 2021)

    Meet NGC 5728, a spiral galaxy around 130 million light-years from Earth. This image was acquired using Hubble’s Wide Field Camera 3 (WFC3), which is extremely sensitive to visible and infrared light. Therefore, it beautifully captures the regions of NGC 5728 that are emitting light at those wavelengths. However, there are many other types of light that galaxies such as NGC 5728 emit, which WFC3 can’t see.

    In this image, NCG 5728 appears to be an elegant, luminous, barred spiral galaxy. What this image doesn’t show, is that NGC 5728 is also a monumentally energetic type of galaxy, known as a Seyfert galaxy.

    Powered by their active cores, Seyfert galaxies are an extremely energetic class of galaxies known as active galactic nuclei (AGNs).

    There are many different types of AGNs, but Seyfert galaxies are distinguished from other galaxies with AGNs because the galaxy itself is clearly seen.

    Other AGNs, such as quasars, emit so much radiation that it is almost impossible to observe the galaxy that houses them.

    As this image shows, NGC 5728 is clearly observable, and at visible and infrared wavelengths it looks quite normal. It is fascinating to know that the galaxy’s center is emitting vast amounts of light in parts of the electromagnetic spectrum that WFC3 just isn’t sensitive to! Just to complicate things, the AGN at NGC 5728’s core might actually be emitting some visible and infrared light – but it may be blocked by the dust surrounding the galaxy’s core.

    Text credit: ESA (European Space Agency)

  13. A resource for discussing the scale of the universe.

    • NASA > APOD > “Great Debates in Astronomy

    The Scale of the Universe (1920); Curtis, Shapley

    The Distance Scale to Gamma-ray Bursts (1995); Paczynski, Lamb

    The Scale of the Universe (1996); Tammann, van den Bergh

    The Nature of the Universe (1998); Peebles, Turner

    Life in the Universe (2020) Many contributors

  14. Video #22 in Sean Carroll’s 2020 chat series is a useful overview, historical recap, and tutorial on the major topics and (technical) language of modern cosmology.

    He notes that “cosmology really brings together a lot of different ideas from a lot of different areas of physics.” And that cosmology has evolved from being somewhat disreputable to an integral part of physics.

    It’s really one of the triumphs of modern cosmology. You know, I remember again when I was in grad school, cosmology was in the process of going from slightly disreputable to a really central part of modern physics.

    Other points include the role of the scale factor (a) in mathematical models. Cosmic thermal history. Inflation is a working hypothesis – a 50% chance of being true.

    He mentions misperceptions of what it means for the universe to be expanding over time. (And I wonder if it’s space expanding or spacetime expanding?)

    He considers the evidence for “dark matter” to be solid (albeit it’s “too broad a category”) – not just the motion of spiral galaxies and gravitational lensing; but, in particular, the CMB.

    And “vacuum energy doesn’t decay away.”

    He concludes:

    We’re still learning a lot about the early universe. I am optimistic … [about] this mystery that we have: why the universe is made of the stuff it is, where it started from, why it looks the way it does.

    • YouTube > Sean Carroll > The Biggest Ideas in the Universe > #22 “Cosmology” (Aug 18, 2020)

    Description: This is Idea #22, “Cosmology.” Perhaps more a field of study than an “idea,” but it is made possible by an extremely powerful idea: that our universe is uniform and simple enough to be understandable [“the ultimate spherical cow”]. We go through the expansion of space, the thermal history of what makes up the universe, and a bit about dark matter and the cosmic microwave background [CMB].

    Blog post: Surely one of the biggest ideas in the universe has to be the universe itself, no? Or, as I claim, the very fact that the universe is comprehensible – as an abstract philosophical point, but also as the empirical observation that the universe we see is a pretty simple place, at least on the largest scales. We focus here mostly on the thermal history – how the constituents of the universe evolve as space expands and the temperature goes down.

  15. Revisiting past research and studies with better instruments and better modeling often refines prior results (like improved measurement of the CMB). But sometimes the revisit yields surprises. Dwarf galaxies are a case in point.

    • Phys.org > “Astronomers discover strangely massive black hole in Milky Way satellite galaxy” by University of Texas at Austin (December 1, 2021) – a combination of better data and supercomputer simulations yields a startling result

    Astronomers at The University of Texas at Austin’s McDonald Observatory have discovered an unusually massive black hole at the heart of one of the Milky Way’s dwarf satellite galaxies, called Leo I.

    For their observations, they used a unique instrument called VIRUS-W on McDonald Observatory’s 2.7-meter Harlan J. Smith Telescope.

    The team decided to study Leo I because of its peculiarity. Unlike most dwarf galaxies orbiting the Milky Way, Leo I does not contain much dark matter. … They also wanted to know whether their profile measurement would match previous ones made using older telescope data combined with computer models.

    When the team fed their improved data and sophisticated models into a supercomputer at UT Austin’s Texas Advanced Computing Center, they got a startling result [that you need a black hole at the center].

    … “there is no explanation for this kind of black hole in dwarf spheroidal galaxies,” Bustamante [UT Austin doctoral graduate María José Bustamante] said.

    The result is all the more important as astronomers have used galaxies such as Leo I, called “dwarf spheroidal galaxies,” for 20 years to understand how dark matter is distributed within galaxies, Gebhardt [UT astronomer] added.

    See also:

    • Space.com > “Giant black hole inside a tiny satellite galaxy of our Milky Way defies explanation” by Tereza Pultarova (Dec 3, 2021) – “There is no explanation for this kind of black hole in dwarf spheroidal galaxies.”

    The Leo I dwarf galaxy, some 820,000 light-years from Earth, is only about 2,000 light-years across. Until now, astronomers thought the galaxy’s mass was about 15 to 30 million times the mass of our sun.

    And if this research is correct, then the estimated mass changes?

    So, implications for other dwarf galaxies? Better data better models … a new dark (invisible) matter ratio?

  16. Another interesting study of dwarf galaxies. This article provides some insight into how mass ratios are modeled by measuring rotational speeds of gas, not just stars, in galaxies: “a graph showing the distance of the gas from the center of the galaxy on the x-axis and the rotation speed of the gas on the y-axis.”

    • Phys.org > “Evidence emerges for dark-matter free galaxies” by Royal Astronomical Society (December 6, 2021)

    When Pavel Mancera Piña (University of Groningen and ASTRON, the Netherlands) and his colleagues discovered six galaxies with little to no dark matter, they were told “measure again, you’ll see that there will be dark matter around your galaxy”. However, after forty hours of detailed observations using the Very Large Array (VLA) in New Mexico (United States) [in 2020], the evidence for a dark matter-free galaxy only became stronger.

    The galaxy in question, AGC 114905, is about 250 million light-years away. It is classified as an ultra-diffuse dwarf galaxy, with the name ‘dwarf galaxy’ referring to its luminosity and not to its size. The galaxy is about the size of our own Milky Way but contains a thousand times fewer stars. The prevailing idea is that all galaxies, and certainly ultra-diffuse dwarf galaxies, can only exist if they are held together by dark matter.

    So, the question is why – exploring possible explanations (see article) for the discrepancy with theoretical predictions.

  17. The Dark Energy Survey

    Another cosmic image witnessing the dynamic and evolving landscape of galaxies.

    • Phys.org > “Galactic ballet captured from NSF’s NOIRLab in Chile” by National Optical-Infrared Astronomy Research Laboratory (May 6, 2022)

    (image description) The interacting galaxy pair NGC 1512 and NGC 1510 take center stage in this image from the Dark Energy Camera, a state-of-the art wide-field imager on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory, a Program of NSF’s NOIRLab.

    NGC 1512 has been in the process of merging with its smaller galactic neighbor for 400 million years, and this drawn-out interaction has ignited waves of star formation and warped both galaxies.

    Credit: Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), J. Miller (Gemini Observatory/NSF’s NOIRLab), M. Zamani & D. de Martin (NSF’s NOIRLab)

    Funded by the US Department of Energy (DOE) with contributions from international partners, DECam was built and tested at DOE’s Fermilab, where scientists and engineers built a “telescope simulator” — a replica of the upper segments of the Víctor M. Blanco 4-meter Telescope—that allowed them to thoroughly test DECam before shipping it to Cerro Tololo in Chile.

    DECam was created to conduct the Dark Energy Survey (DES), a six-year observing campaign (from 2013 to 2019) involving over 400 scientists from 25 institutions in seven countries.

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