Given how long stars live in comparison to human lifetimes, I always do a double-take at science fiction tales of starships dropping in to study a nova just as it’s about to go off. I suppose we have to assume the starship civilization has found a way to time such matters. There’s a Star Trek: The Next Generation episode that involves rescuing a planetary population from a star that’s about to explode (“A Fury Scorned”), but of all the nova arrivals, I like Samuel Delany’s 1968 novel Nova the best. Here, in order to harvest a rare element dubbed ‘Illyrion,’ the exact moment of the explosion has to be known and exploited through a mind-bending run through the debris.
Today’s paper doesn’t involve a nova, but it does involve a star that is doing things on a very short timeframe indeed. The star is known as Sakurai’s Object (V4334 Sagittarii). Japanese amateur Yukio Sakurai observed the object in 1996, noting how it appeared to be brightening. A 1976 detection of the progenitor star had recorded a magnitude of 21, whereas when Sakurai tagged it, it had reached magnitude 11. The apparent eruption here was first thought to be the result of a nova, but that was discounted for spectral reasons.
Several years later the unusual brightening began to decline. That was evidently the result of loss of mass and subsequent condensation of stellar material, which wound up hiding the star behind a dusty screen. It now shows a spectrum similar to what is known as a Wolf-Rayet star. Sakurai’s Object appears, however, to be in the much less massive Wolf-Rayet class known as a [WR] star. A conventional Wolf-Rayet star is massive, stripped of its hydrogen by huge stellar winds that leave the underlying helium-burning layers exposed. The odd [WR] notation turns out to be needed because low-mass objects like these can mimic a Wolf-Rayet star, so it was necessary to show that this is a different kind of object and a much smaller kind at that, though with Wolf-Rayet features.
There are also sub-categories of [WR] including [WC] that don’t need to occupy us now, although the paper explains what they mean. What’s intriguing about Sakurai’s object is its pace. According to current calculations it’s now roughly 6 times hotter than it was 30 years ago, and is climbing back toward the white dwarf temperatures it had before the eruption that made it observable by Sakurai. Albert Zijlstra (Jodrell Bank Centre for Astrophysics, University of Manchester), describes its significance:
“Most stars evolve so slowly that major changes take place over timescales far longer than a human lifetime. As a result, we usually have to piece together snapshots of stellar evolution by comparing different stars at different stages of their lives. Sakurai’s Object offers something far rarer. It is one of the very few stars known to have changed dramatically within just a few decades, giving us the opportunity to watch stellar evolution unfold in real time. With our observations, we can test theories of how stars evolve and gain new insights into one of the shortest and least understood phases in the life of a dying star.”
Image: The rapid brightening of Sakurai’s object allows astronomers to study the final phases of the stellar evolution in only a few decades. The left and right panels show the brightening. The middle panel is an image obtained with the radio telescope ALMA, showing the material ejected after the star re-ignited. The material currently extends over a size similar to our entire solar system. Credit: Stefan Kimeswenger, University of Innsbruck; Peter van Hoof, Royal Observatory Belgium. The observatory also has a short video showing the brightening.
What we apparently have here is a star once similar to the Sun that had finished its nuclear burning and was in the process of turning into a dense white dwarf star about the size of the Earth. But an event known as a ‘very late thermal pulse’ seems to have occurred. This happens when helium deep inside the star reignites, forcing a rapid expansion along with the ejection of stellar materials, so that the star has, at least for the time being, been reinvigorated. Along with another star called V605 Aquilae, Sakurai’s Object is one of only two stars that have been directly observed going through this process.
Let me turn to the paper to home in on the matter of thermal pulses:
Depending on when the pulse occurs, it is classified as an AGB final thermal pulse (AFTP), a late thermal pulse (LTP; post-AGB), or a very late thermal pulse (VLTP; see M. M. Miller Bertolami 2024). In the most extreme case (VLTP), the star is already on the white-dwarf cooling track when the flash causes rapid expansion and cooling, accompanied by substantial mass ejection into the circumstellar environment. The star is thus “born again” and returns close to its former AGB position in the HR diagram. Subsequent evolution involves reheating, and possibly an additional cooling excursion, as the star evolves back towards the white-dwarf domain with a markedly altered surface composition (T. M. Lawlor & J. MacDonald 2003).
No wonder this was a hard object to observe. The ejected gas and dust following the 1996 outburst caused the star to became hidden to direct imaging. Low density gases are coming off the star even as the outflowing atmosphere, moving at e 500 kilometers per second, is optically thick. Much of the spectrum produced is nebular. The team compared data from the VLT with computer models originally developed to study the processes that power the atmospheres and winds of Wolf-Rayet stars. The emission lines studied in this paper are embedded in the stellar wind, as opposed to the ejecta and dust. Much of the credibility of the analysis depends upon separating these factors.
The analysis reveals a stellar temperature at the surface pegged at between 27,000 and 36,000 degrees Kelvin. Scientists will now be able to study the process of the reheating following the eruption that occurred thirty years ago. Early indications are that the process is occurring more slowly than some models had predicted, so that Sakurai’s Object becomes a useful laboratory, like V605 Aquilae, into stellar behavior in this extremely rare class of stars. At some point, Sakurai’s Object will return to its fate as a white dwarf, only now under close observation as we ponder massive changes in a very short order.
Griet Van de Steene (Royal Observatory of Belgium), a co-author of the paper adds:
“Sakurai’s Object evolved much more quickly than pre-existing models for stellar evolution predicted. This led to a new generation of models that we now need to test. Our measurements show that the star is reheating more gradually than some of these new models predicted. That gives us an important way of testing which theories best describe what happens when a dying star briefly springs back to life. As we continue to monitor the star over the coming years, we expect to learn much more about this remarkable phase of stellar evolution.”
The paper is Marcolino et al (2026). The emergence of a [WC] star in Sakurai’s object. Monthly Notices of the Royal Astronomical Society, 552(1), Article stag1533. Full text.
Perhaps this type of object or event is extremely common, or even a normal stage in the evolution of ordinary stars! They only seem rare and mysterious because the outburst is over quickly, faint, and astronomers are rarely observing it when it occurs.
Think of it as a form of cosmic hiccups, or flatulence.
Yes, indeed. It is expected that between 10% to 20% of all low-mass stars that evolve, more or less, in isolation will experience these “hiccups”. But it is very difficult to catch one because they last very little
I wonder if the Vera Rubin telescope will detect a lot more stars that change in brightness over short periods of time as it scans the southern skies, creating a time-lapse record of the sky. Will it find more stars like that Wolf-Rayet [subtype?] in the post, or other new types yet to be classified?
There is great variability in variability. Some variable stars oscillate in strict and predictable sinusoidal patterns, sometimes several of them simultaneously! Others are erratic and chaotic, or even accidental (a sudden outburst and then nothing…). And even in the most regular oscillators, there are huge differences in their periods–sometimes hours, sometimes years. Some variable behavior is shared by many in their class (RR Lyrae and the Cepheids, for example). Presumably, the variability is due to some condition in their interiors shared by many other stars. But others are unique.
And what about the flare stars? How do they fit into this taxonomy? And what about those who blink on and off because they are eclipsed or transited by other bodies orbiting them? They are not true variables but they can mimic them.
It would be difficult to design an instrument that could detect all these types, given the great differences and time scales of variable star behavior.
Historical Note: In the olden days, an instrument called a ‘blink comparator’ was used because it could detect motion or brightness changes between two photographs. It was used by Clyde Tombaugh to discover Pluto. The comparator was equipped with a rotating shutter that allowed the operator to view one photograph, then the other, through a microscope–repeatedly. If anything in the star field was moving or changing brightness it stuck out dramatically. Unfortunately, choosing the correct time interval between the two
exposures is critical, and requires some prior knowledge of what you’re looking for. My guess is its all automated now.
@Henry
Astronomers must have had some way to determine which stars were the same class as others and which were new. Given the stars we have classified, can we not use machine learning to discriminate between these classes and even find cases that do not fit the existing classifications? With the abundance of new observational data, wouldn’t this be worth trying, if only to allow focusing on stars that need to be observed with different instruments to classify them and find anomalies for further observation?
Hi, Alex
There IS a way to classify stars: the color-magnitude, or Hertzsprung-Russel, diagram–astronomy’s answer to the chemist’s Periodic Table. And it is still very much in use today. The diagram plots magnitude as a function of temperature. Different types of stars occupy different parts of the diagram, and can move around in the data space as they evolve. Throughout most of the twentieth century stellar astronomy has been about using that data, plus the theoretical physics of thermonuclear reactions and radiative transfer in plasmas, to come up with a reasonable idea as to how stars evolve. It is one of the triumphs of twentieth century astronomy.
Most stars settle down after forming and occupy a spot on the Main Sequence (an arc slashing across the H-R diagram) and they stay there until they start running out of nuclear fuel. This process is much faster for massive stars. Unfortunately, neither mass nor age can be directly measured, they must be derived theoretically,
The two axes of the diagram, brightness and temperature, are both measurable quantities, so once you can determine a star’s magnitude and color (stars are black-body radiators so surface temperature and color are correlated), its position on the diagram is established. As you know, the main color classes, listed from hottest to coolest, are O, B, A, F, G, K, and M. There are other classes, and each class can be further subdivided using minute details in the spectrum. But most stars spend most of their lives on the Main-Sequence.
Its really critical that non-astronomers read up on the color-magnitude relation. Most astrobiology enthusiasts know a bit about it, but a deep immersion is necessary. Without it you can’t really know HOW astronomers know WHAT they know about stellar structure and evolution. What they know is one of the triumphs of science, but there are still many unanswered questions.
Those not familiar with the H-R diagram should beware: Magnitude, on the Y axis, increases going up, but bigger magnitudes mean fainter stars. And its not linear, magnitude is a power function we inherited from the Ancient Greeks. On the X axis, the cooler M stars are on the right, and the hotter near the origin. Its confusing, I know, but there are obscure historical reasons for these weird conventions and now we’re stuck with them.
What a peculiar environment! I was asking Google AI a series of questions with ever stranger answers just now. I didn’t understand how this object changes brightness in decades when it takes light 100,000 years to get out of the sun. I haven’t checked everything, but apparently the He shell is a moderate distance into the star, 100 miles or less, with a layer of hydrogen over it. The degenerate matter under it doesn’t expand with heating and stays the same throughout the whole process. The helium detonates and blows off into space.
But how does the star reset then? Well, apparently there is a “hydrogen ingestion flash”. The hydrogen in the outermost shell goes INWARD during the explosion by some magic of convection. Then, instead of taking billions of years to fuse, 80% of the ingested hydrogen can become helium or other elements in … FIVE MONTHS. I was sure the AI had found the virtual magic mushrooms this time, but it seems to check out. In concept, I think, an advanced civilization could hang out around a star like this, resetting it with hydrogen, salting with some C-13 or other neutron rich isotope, and forcing it to blast out vast amounts of gold, platinum, rare earths etc.
I can only imagine the awesome scale of that mining operation and the politics of regulating such operations. I wonder if such operations could be determined to be by ETI?
Paul, The 0.6 solar mass white dwarf that our sun is expected to form once it goes through the red giant phase is around ~twice the diameter of the Earth, more like a super earth or mini Neptune. A ~1.4 solar mass one is around the size of the moon ! I have asked if they will be putting the Nancy/Roman images on Aladinlite, it would be great to see all these images of the cosmos in one place. Once our sun goes through the red giant phase it will be insanely hot for millions of years, plenty of time for an intelligent civilisation to move back in.
I’ll have to disagree with you there, Michael. Every source I’ve checked sees a white dwarf from a source like the Sun coming in at about the same diameter as the Earth. I didn’t realize there was any disagreement on this, so I’m interested in the discrepancy.
A 1 solar mass white dwarf is about the radius of the Earth but our sun will dump around 40 % of its mass leaving a 0.6 solar mass WD. I can’t seem to post links for some reason which would show via a image the relationship between mass and radius.
This link indicates that the size of a WD is inversely related to its mass.
https://www.researchgate.net/figure/Mass-radius-relations-of-white-dwarfs-obtained-with-the-Chandrasekhar-EoS-dashed-black_fig4_282692063
https://dq0hsqwjhea1.cloudfront.net/Earth-and-white-dwarf-comparisons_ST.jpg
This should do it, Sirius b is about 1 sol mass. Van Maanens star is around 0.67 solar masses, which would be closer to our sun at the end of the red giant phase.
Sakurai’s object has a very similar mass to the suns white dwarf when it evolves, so we can expect the same result. It’s burning with 10000 luminosities of the sun during this phase !. That could allow aliens to more inwards very easily.
@henry
When I suggested using the Vera Rubin telescope to identify variable stars, you stated that there are so many different rates and sizes of variability that this would be hard to do. What I wanted was an explanation of how different types of variable stars were initially identified, with the “That’s funny, I wonder what it is?” thought process that astronomers went through to distinguish between different types. Ancient astronomers could detect the rapid brightening of a star that we now call a supernova. Better telescopes allowed us to detect novae. Radio allowed the detection of pulsars, which we can now explain.
RR Lyrae stars were discovered in the last decade of the 19th century. Cepheids were discovered in the first decade of the 20th. How were these 2 type distinguished as being different types? Transits need high-resolution light and time data to be distinguished, not something the VR telescope can detect. The Wolf-Rayet stars were detected even earlier in the mid-19th century due to their unusual spectral emission lines.
V4334 Sagittarii, the subject of this post, was thought to be a nova, but this hypothesis was discarded for reasons not explained.
The VR telescope should be able to detect many stars that have variable timescales of changing brightness, many not observed in the past, although coupled with the reexamination of old photographic plates, very long periods of variability may be detected.
The VR telescope will be another source of Big Data that becomes a treasure trove for new discoveries, including stars that are variable in some way. Increasingly powerful computers and algorithms are the means to be able to extract “needles in haystacks” from such data, which can then be the targets for astronomers looking at such phenomena.
The different classes of variables where first identified by the shape of their light curves, that is, the shapes of the graphs where magnitude was plotted as a function of time. The brightness of the stars was noted on each date by astronomers (usually amateurs) which communicated their observations to coordinating organizations (such as the American Association of Variable Star Observers). The AAVSO then compiled and published these charts for their use by professionals. It was quickly noted that the light curves were not all sinusoids. However, they had distinctive shapes; for example they might consist of a slowly rising
slope followed by a fast, precipitous drop–then repeat. Another example: an eclipsing binary is not a true variable, but its light curve is immediately recognizable; a straight line with alternating dips (eclipses) of different width and depths. I imagine this could be done with AI these days, sparing astronomy grad students endless hours of drudgery.
This type of analysis, simple as it seems, can sometimes yield phenomenal insights. The Cepheids are probably the most famous. Easily recognizable from their distinctive light curves, it was quickly noted that the period and luminosity were correlated. Since a few
nearby Cepheids had known distances (perhaps by parallax measurements), it was possible to precisely calibrate the period-luminosity relationship so if you could identify it as Cepheid you could get its distance. Bang!
This is how Hubble proved Andromeda was another galaxy. He was able to identify bright Cepheids in the galaxy, measure their light curves, and prove immediately by calculating their true brightness that they were very distant. It was not a nearby nebula.
Many variables are erratic, and their light curves are random noise, but some can be investigated statistically. And I would suggest many random episodes occur, perhaps even frequently, but are never noticed because that old photographic patrol plate in the archive has never been looked at.
Yes, it would be wonderful if this process could be automated.
A big challenge is attaining the observational data. A star may wax and wane but you need data at various points in its brightness cycle to have an opportunity to discover its variability, whether the comparison is done by technology or humans. I believe a lot of variable stars have historically been discovered almost accidentally by searches for other things, such as planets, comets and asteroids. Perhaps using those blink comparators already mentioned.
Once variability is identified the star becomes a candidate for closer observation to determine whether the variability is real or due to observation error, and then to categorize the star in the manner Henry describes. A near continuous stream of data is needed to plot the brightness curve and to determine whether it’s erratic or a repeating cycle.
New instruments now online or planned that watch and record a wide area of the sky for long periods (continuous or at intervals) give us the needed data. A lot of variable stars may be discovered and categorized, for example, in the ongoing search for exoplanets, as a byproduct of the search even if not the primary objective. The data will at least become available for those interested in doing those secondary searches.
Another historical anecdote:
Organizations that coordinate amateur observing programs with professional data collection requirements (such as the AAVSO) scan the literature, or receive requests from researchers, for stars that are suspected to be variable and publish finder charts for the convenience of “citizen scientists”. These charts are available for naked eye variables as well as the faintest, reachable only by the largest amateur apertures. The charts show the star and the surrounding field with the accurate magnitudes of nearby field stars. Amateurs engaging in the observing program visually observe the star, determine its magnitude by comparison with its neighbors, and then report their observation to the collecting authority. At any time, many amateurs throughout the world, by logging several stars in one night, contribute to a database of many variables and a magnitude estimate for one moment in time for each star. These collected observations are binned for each star, and resulting plots (magnitude vs date) are published. Each dot is one observation, and the spread in the brightnesses give the analyst an idea of the error bars for each individual observation.
If the variable exhibits regular periodic behavior, the charts may span decades of observations, with the X-Axis reflecting the fraction of the period rather than a specific date and time. This sort of of tedious data collection is suited for amateurs and their equipment, but is a great convenience for the professionals, which are provided with a graphic document which often reveals vital insights just by a quick glance at the plotted curve. Many variables have distinctive light curve shapes that can be easily recognized and unambiguously identified.
I’m sure that much of the satellite and digital technology used to detect transients, novae and exoplanets can be used for this work.
some other info :
https://iopscience.iop.org/article/10.1086/310241/fulltext/
finally, what does this object teach us in our knowledge of the universe?
OT
I got a reply from astro.unistra.fr regarding the NGR Space telescope images,
‘The Nancy Grace Roman Space Telescope is currently in commissioning phase, on its way to L2. First public science images are expected early 2027.
As Roman will not have a proprietary time for the main surveys, I expect some Roman images to be available in Aladin in the first half of 2027.’
https://aladin.cds.unistra.fr/AladinLite/
It would interesting how AI could be put to use on the enormous amounts of data that will be available to the public.
This should be worth waiting for !
Interesting if you put V4334 Sagittarii into Aladin in allwise mode you can see a glowing orb, not sure it’s a image effect or it actually looks like an outburst.
Strong IR? If so, I would have thought that would be unusual for such a hot star, given its low visibility in the optical. Perhaps a local warm object occluded the star?
I’m pretty sure I already submitted the following material to Centauri Dreams sometime in the recent past. But I believe this is useful information, and in case you missed it, here it is again. Take this brother, may it serve you well,
—
Today I ordered the 2027 edition of the Royal Astronomical Society of Canada Observer’s Handbook.
The RASC Handbook is published yearly and is a sort of almanac with ephemeral data useful to amateur astronomers, but it is compiled with a detail and depth of value to professionals as well. Along with the ephemera (data which changes from year to year, like sunrise and sunset tables) it also contains many articles and listings of specific topics which are repeated yearly, but updated when new information is developed by ongoing research. Features on events of special interest are also included. There are tables of astronomical constants and observing tips. Even old editions are nice to keep around. There is plenty of material there to entertain you when you feel the need for reading material. I keep old copies in the bathroom, or give them to my friends. You don’t need to be an astronomer to treasure the Handbook, anyone with an interest in science will enjoy perusing it.
One of my favorite articles is “The Nearest Stars” by Todd J. Henry, which lists every known star within 5.0 parsecs (16.3 light-years). These are the closest known objects to the Sun, the ones we know the most about, and whose data has been determined to the highest precision. It is a detailed look at the solar neighborhood, and a useful sample of space in this corner of the galaxy. This a field of intense research and the list is updated frequently, and kept up to date.
The list contains 53 known systems comprised of 66 stars, 9 brown dwarfs and 13 known extrasolar planets. This catalog is constantly being updated by new observations, so I guess you could call this data “ephemeral”. Many of these guys are extremely faint, so new ones are turning up all the time. The brightest is Sirius (apparent magnitude -1.43). The faintest, Wise 1049-5319 B (apparent magnitude 24.07). They are also the intrinsically brightest and faintest, respectively. the nearest is Proxima Centauri (4.24 ly), the farthest, Omicron 2 Eridani (16.3 ly).
Forty eight of these stars are red dwarfs, spectral class M. Spectral classes O and B (the hottest) are totally missing from the list, and there is only 1 A and 1 F represented, the next lowest temperatures. Two share our Sun’s spectral class, G, while 8 are class K. (The spectral classes, from hottest to coolest are O,B,A,F,G,K,M.) The 5 white dwarfs, ancient, dying stars that have completed their evolution, are classed separately. The brown dwarfs are not stars at all, they glow from gravitational contraction only, they are too light and cannot maintain thermonuclear reactions in their cores.
These stars are listed in a table, with their names, positions, parallaxes (positions), proper motions (velocity across the line of sight) and radial velocity (towards or away from us), their apparent magnitude (how bright they appear) and their absolute magnitude (how bright they would appear at a standard distance of 10 pc). Also listed are their position angles (if they are binaries) and their spectral classes. Some of these fields are left blank, this field is still rapidly expanding.
This is what most of the Galaxy looks like, or at least the spiral arms and the disk. The brightest, hottest stars are also young, and the most short-lived, they can be seen at enormous distances, but they are extremely rare, even though they comprise much of the naked eye sky. The big red giants also are visible from afar, but they too are rare, and they are near death. The sample in this list is representative. It represents where we live.
The sky is like the sea, it contains whales and fishes, but most of the biomass is in the plankton.
@henry
What is the form of matter in the sky that is equivalent to plankton? [exclude dark matter]
I would have guessed stars, and if so, what type?
What I meant was that most of the naked eye stars we see are very bright, but very far away. But by far, the most numerous stars are very faint dwarfs (red and white), but none are bright enough or close enough to be seen without optical aid.
Of the 75 stars and brown dwarfs in the RASC Handbook list (<5 pc away) 48 are red dwarfs. There are probably others, as well, they just haven't been identified.
My lame attempt to come up with a poetic metaphor is just another way of saying that the bulk of what is out there is just too faint to be seen without telescopes and photography. A census of the stellar population based solely on what we can see without optical aid would be heavily biased towards stars that are actually a rather small minority of the population, the rare but bright ones
that can be seen at great distances.
I know I seem to flog this particular dead horse a lot, but one of the problems we have at cataloging any kind of inventory of objects in astronomy is that the selection effect (some object types are easier to detect than others) skews our perception of the population.
For example, our ever-growing exoplanet lists seem to be crowded with objects that are easier to detect so the observed
distribution is biased. It may turn out that earthlike planets are actually in the majority, but we just don't have the technology to see them and gauge their true numbers. Right now we are in danger of being misled that most exoplanets are massive gas giants in highly elliptical close orbits around very low-mass stars. This conclusion may be dead wrong.
@henry
I tried to get an answer to my question using the stellar type and mass ranges from the Wikipedia page on stars supplemented with an upper-bound mass for O stars from this site.
For a crude approximation, I ran the data using either the upper or lower bound mass values, using a random sampling of 100,000 stars based on their probabilities. [Despite their mass range, O stars are so rare that they are not sampled at all.]
With the upper-bound values, M_dwarfs are clearly the bodies with most of the mass:
O 0.0
B 1888
A 1396
F 4278
G 7979
K 9288
M 34296
With the lower-bound masses, the picture is more nuanced with the GKM stars all having about the same total mass, and the F stars about 1/2 their cumulative mass.
O 0.0
B 247
A 930
F 3178
G 6138
K 5224
M 6097
I would need to spend time working on a distribution for mass ranges, but I think it is fair to say that M_dwarfs may well have most of the mass.
I assume that, as in our planetary system, planets are a mere fraction of their primary’s mass. I do wonder whether brown dwarfs might be far more numerous than we think, and therefore possibly contain more of the mass. Probably not, but this is way beyond my current knowledge. I also assume that the gas clouds do not represent most of the mass in a galaxy, but that seems unlikely.
Hi, Alex
You bring up some excellent questions which I, frankly, do not know how to answer, at least not quantitatively. Some of them, I fear, no one knows how to answer! All we know for certain is that M dwarfs make up the vast majority of all stars, both in total number and by cumulative mass (as you point out). That much is certain, but assigning numbers to that is problematic.
But answering some of your concerns is further complicated by several additional factors.
1) Not all M stars are red dwarfs, spectral classes are based on surface temperatures, not necessarily their evolutionary history.
The relatively short-lived, highly evolved, bright, massive, hyperactive red supergiants are class M too.
2) Low-mass red dwarfs are much more likely to form than other, more massive stars, but they also live much longer than heavier stars, so their total numbers, both absolute and proportional, are skewed by the fact that once they form, they live practically forever.
3) More massive, hotter, bluer stars (‘early’ spectral classes in astronomical jargon) are more interesting and get more attention from researchers. They are also brighter, easier to study and can be observed effectively at greater distances.
4) Red dwarfs are not evolving, other than an occasional flare, they are pretty stable and tend to stay that way. Until they became interesting from an astrobiological perspective, they attracted less scrutiny.
5) Brown dwarfs have only recently been identified as a class of stellar object. Their proportion of the entire stellar population and their significance to the big picture is still not well understood.
As my plankton vs whale analogy attempted to point out, those citizens who attract the most attention are not necessarily the ones of greatest significance.
I would like to continue this discussion, you ask the most cogent questions! Is there any way we can communicate directly? Perhaps Paul can give you my phone number or email address. I will authorize him to release them to you.
@henry
Thank you for the note on the issue of fuzziness in stellar classifications. Whether this makes any difference to the computations, I don’t know. Given the likely skewness in mass distributions, the use of lower-bound masses may be closer to the real ratios than the upper-bound masses.
I ran a test of Brown Dwarfs vs M dwarfs. Using the BD minimal mass > 13 Mj -> ~= 0.01 Sun, and a maximum of 0.08 (the lower bound of an M dwarf)
For BD > M dwarf, the ratio of BD: M dwarf is ~= 10:1 – 5.5:1
This implies that BDs must be very common, and on average closer to us than Proxima, rather like the idea that rogue planets may be similarly common. If so, they should have shown up with IR astronomy surveys, but AFAIK, this is not the case. The following quote from Wikipedia seems to confirm that BDs are less common than M dwarfs, and therefore M dwarfs are likely the dominant class regarding cumulative mass.
From Wikipedia on “Brown Dwarf”:
[These simple calculations are part of what I think of as understanding the context of numbers, in this case, what type of object dominates the ordinary mass of the galaxy/universe. In the distant future, if the universe is not closed, cooling red dwarfs will likely mean that the Milky Way will look red to sapient eyes, with perhaps a few hotter stars that have more recently formed.