The Milky Way's Unfinished Feast

The Slow Unmaking of the Sagittarius Dwarf Galaxy

How our Galaxy is dismantling a smaller neighbour, scattering its stars across the heavens, and revealing the turbulent history concealed within the Milky Way itself.

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Translation: This article may be read using the translation facility provided on this website. Machine translations may not always reproduce the precise scientific meaning, nuance or idiom of the original English text.

Foreword

There is a curious tendency in popular imagination to regard galaxies as permanent fixtures of the Universe: vast islands of stars, serenely rotating through the darkness and enduring with scarcely a change from one age to another. Nature, however, is seldom so obliging. Galaxies are not monuments. They grow, collide, consume, shed material and are themselves transformed by the gravitational influence of their neighbours.

The Milky Way is presently providing us with a remarkable demonstration of this cosmic reality. A smaller companion, the Sagittarius Dwarf Spheroidal Galaxy, is being progressively dismantled by the gravitational field of our own Galaxy. Its stars are being drawn away from their original home and stretched into immense stellar streams that extend around the Milky Way.

This is not destruction in the cinematic sense. There is no explosion, no sudden obliteration and, contrary to popular imagery, almost no direct collision between individual stars. It is a far more subtle affair: gravity patiently rearranging the architecture of a galaxy over billions of years.

For me, the subject possesses a particular fascination because it demonstrates something fundamental about astronomy. The sky is not merely a collection of objects arranged at immense distances. It is a historical record in motion. Every stellar stream, orbital disturbance and chemical signature may preserve a chapter from the Milky Way's long and turbulent biography.

This spirit of inquiry also accords with the scientific obligation expressed in Article 51A(h) of the Constitution of India, which calls upon every citizen:

“to develop the scientific temper, humanism and the spirit of inquiry and reform.”

The story of Sagittarius is therefore not simply about one small galaxy losing a struggle against a larger one. It is also about how astronomers reconstruct invisible history from faint stars scattered across the sky.

About the Author

I am Dhinakar Rajaram, an independent writer and lifelong student of science with a particular affection for astronomy and the physical sciences.

My interest in the heavens has never been confined merely to identifying planets, stars or constellations. I have always been drawn to the larger questions: how celestial systems evolve, how apparently stable structures conceal violent histories, and how modern observation permits us to reconstruct events that occurred long before humanity existed.

As an amateur astronomer, I have found that even modest observations of the night sky encourage a salutary sense of proportion. The objects we observe may appear tranquil through an eyepiece, yet many belong to systems undergoing processes of extraordinary violence and transformation.

The Sagittarius Dwarf Galaxy is one such example. It reminds us that our Milky Way is not a passive observer of the Universe. It has a history of mergers and accretion, and that history has not yet ended.

Preface: A Galaxy Being Taken Apart in Plain Sight

The phrase “galactic cannibalism” is dramatic, and perhaps a little mischievous, but it conveys a genuine astronomical process.

Large galaxies grow partly by absorbing smaller galaxies. In the modern cosmological picture, galaxies are assembled hierarchically. Smaller structures merge, interact and contribute their stars, gas and dark matter to larger systems.

The Milky Way itself is the product of such a history.

Among the clearest examples of this continuing process is the Sagittarius Dwarf Spheroidal Galaxy, generally abbreviated as Sgr dSph. It is a satellite galaxy of the Milky Way and has been subjected to repeated gravitational encounters with our Galaxy.

During these encounters, Sagittarius has lost substantial quantities of material. Stars that once belonged to the dwarf galaxy now travel along enormous orbital pathways around the Milky Way, forming what astronomers call the Sagittarius stellar stream.

In other words, Sagittarius is gradually becoming less of a distinct galaxy and more of a population of stars distributed through the gravitational domain of the Milky Way.

Yet there is an important twist in this tale.

Sagittarius has not merely been a victim of the Milky Way. Evidence suggests that its repeated passages have also disturbed the larger Galaxy, producing ripples and vertical motions within the Galactic disc and possibly contributing to episodes of enhanced star formation.

The supposed meal, therefore, has occasionally shaken the dining table.

1. What Exactly Is the Sagittarius Dwarf Galaxy?

The Sagittarius Dwarf Spheroidal Galaxy is a relatively small satellite galaxy associated with the Milky Way. It was identified during the 1990s and quickly became one of the most important laboratories for understanding how large galaxies assimilate smaller companions.

The term “dwarf spheroidal” describes a class of galaxies generally characterised by relatively low luminosity, little or no present-day gas and a broadly diffuse stellar structure.

Sagittarius, however, is no ordinary dwarf galaxy in the astronomical record.

It is unusual because we are observing it while it is undergoing severe tidal disruption.

The galaxy has been stretched and distorted by the Milky Way's gravitational field. Its surviving central body is no longer an isolated and symmetrical system in the conventional sense. Rather, it is the remnant of a once more substantial galaxy whose outer material has progressively been stripped away.

The Sagittarius system also contains a remarkable assortment of stellar populations, preserving evidence of a complicated evolutionary history. Its stars span different ages and chemical compositions, indicating that the progenitor galaxy once experienced a richer and more extended history than its present battered appearance might suggest.

In that sense, the remnant we see today is rather like the surviving portion of an ancient manuscript after many of its pages have been scattered across the world.

2. The Gravitational Contest: Why Sagittarius Is Being Torn Apart

Conceptual illustration: The diagram is not to scale. It represents the manner in which differential gravitational forces can draw stars away from a satellite galaxy, producing extended leading and trailing tidal streams.

To understand what is happening to Sagittarius, one must first distinguish between ordinary gravitational attraction and tidal gravity.

Gravity does not pull equally upon every part of an extended object.

The side of Sagittarius nearer to the Milky Way experiences a somewhat stronger gravitational attraction than the side farther away. Over enormous distances and immense periods of time, this difference matters.

The result is a tidal force.

If the gravitational binding of Sagittarius is insufficient to retain stars in its outer regions, those stars can be removed from the dwarf galaxy and placed into independent orbits around the Milky Way.

Some stripped stars move ahead of Sagittarius along its orbit. Others fall behind. Astronomers therefore speak of leading and trailing tidal tails.

These streams are not necessarily neat, narrow lines. Their structure depends upon the history of the stripping, the internal motions of the original stars, the gravitational field of the Milky Way and the perturbing influence of other massive objects.

The process is, therefore, a form of celestial unravelling.

3. A Slow Destruction Measured in Billions of Years

One must resist the temptation to imagine Sagittarius being destroyed in a single collision.

Galactic interactions operate on timescales that are almost beyond ordinary intuition.

Sagittarius has been orbiting within the gravitational environment of the Milky Way for billions of years. During that long history, it has approached the denser inner regions of our Galaxy and passed through or near the Galactic disc on several occasions.

Each close passage can alter the structure of the dwarf galaxy.

Stars may be stripped away. The surviving remnant may become more elongated. Its orbit may evolve. Material already removed may spread farther along the orbit.

The process resembles neither a demolition nor an explosion. It is closer to the gradual erosion of a coastline, except that the coastline is made of stars and the tide is gravity.

ESA's Gaia observations have helped clarify that Sagittarius has undergone repeated interactions with the Milky Way over billions of years. These passages have progressively reduced the satellite and produced the extensive stellar debris associated with the Sagittarius stream.

The precise future of the surviving remnant is still a matter for dynamical modelling. Astronomers can confidently state that Sagittarius is undergoing disruption; the exact chronology and final stages of that disruption, however, depend upon details of its orbit, mass and the gravitational structure of the Milky Way.

That distinction is important.

Science is strongest when it distinguishes clearly between what has been observed, what has been modelled and what remains uncertain.

4. The Sagittarius Stream: A River of Stars Across the Sky

The most spectacular consequence of Sagittarius's disruption is the formation of its enormous stellar stream.

The stars stripped from the dwarf galaxy do not simply vanish into the Milky Way.

They retain information about their origins.

Because stars removed during similar periods may possess related positions and velocities, astronomers can identify groups of stars that move together through space. Such populations are known as co-moving stellar structures.

The Sagittarius stream has become one of the great archaeological features of the Galactic halo.

It extends over an enormous portion of the sky and represents stellar debris released during different stages of Sagittarius's long interaction with the Milky Way.

There is an important point here which is rarely emphasised in elementary astronomy.

A stellar stream is not merely debris. It is a dynamical measuring instrument.

The path followed by the stripped stars responds to the gravitational potential of the Milky Way. By studying their positions and motions, astronomers can test models of the Galaxy's mass distribution.

This includes one of the most elusive components of the Universe: dark matter.

The stars themselves are visible, but the gravitational landscape through which they travel includes matter that cannot be observed directly through ordinary light.

Thus, a galaxy being dismantled may help us weigh the Galaxy doing the dismantling.

5. How a Stellar Stream Becomes a Galactic Measuring Tape

Conceptual illustration: Stellar streams trace orbital pathways through the Galactic gravitational field. Their shapes and motions can therefore be compared with theoretical models of the Milky Way's visible and invisible mass.

6. Gaia and the Revolution in Galactic Cartography

For much of astronomical history, the principal difficulty in studying the Milky Way was that we lived inside it.

It is rather difficult to draw the map of a forest when one happens to be standing among the trees.

The European Space Agency's Gaia mission has transformed this problem.

Gaia has measured the positions, parallaxes and proper motions of an enormous number of stars. Its observations have permitted astronomers to identify structures that would have been exceedingly difficult to recognise from ordinary images alone.

This is particularly important for stellar streams.

Many stars belonging to the Sagittarius stream are faint and scattered across regions of the sky already crowded with Milky Way stars. Simply photographing the sky does not necessarily reveal which stars share a common origin.

Gaia adds motion to the picture.

Instead of merely asking:

“Where is this star?”

astronomers may also ask:

“How is this star moving?”

That additional information is revolutionary.

A group of stars separated across the sky may reveal its common ancestry because its members possess related motions through phase space.

In this manner, Gaia has helped transform astronomy from a largely static catalogue of celestial positions into an increasingly dynamic map of Galactic motion.

The Sagittarius stream is among the most conspicuous beneficiaries of this revolution in Galactic cartography.

7. The Unexpected Truth: Sagittarius Has Also Disturbed the Milky Way

Here the story becomes considerably more interesting.

One might imagine that a small satellite galaxy approaching the Milky Way would be insignificant compared with the enormous mass of our Galaxy.

That would be an oversimplification.

Repeated passages by Sagittarius appear to have disturbed the Milky Way's disc.

Gaia observations have revealed evidence of complex motions among stars in the Galactic disc, including vertical disturbances and patterns that may be associated with the dynamical consequences of interactions with satellite galaxies.

Sagittarius is considered an important candidate for producing some of these disturbances.

In other words, the Milky Way is not simply swallowing Sagittarius without consequence.

The smaller galaxy has repeatedly delivered gravitational disturbances to the larger system.

The interaction has been compared, conceptually, to ripples spreading through water after an object has disturbed its surface.

The Galactic disc is not liquid, of course, but it can nevertheless respond dynamically to gravitational perturbations.

Stars may be displaced from their previous motions. Gas within the Galaxy may be compressed. Patterns of stellar motion can persist long after the original encounter.

This introduces an intriguing possibility.

The Milky Way's present structure may still contain dynamical memories of encounters that occurred billions of years ago.

Our Galaxy, in effect, carries scars.

8. Could Sagittarius Have Influenced Star Formation?

This is one of the more fascinating developments in the study of the Sagittarius interaction.

Research based upon the star-formation history of regions near the Sun has identified episodes of enhanced star formation whose timing has been compared with proposed passages of Sagittarius through the Milky Way's environment.

The possibility is not that Sagittarius directly created individual stars in any simplistic sense.

Rather, a gravitational encounter may disturb the Galactic gas.

Gas clouds can be compressed.

Compression can encourage gravitational collapse.

Under suitable conditions, collapsing regions may form new stars.

Thus, the interaction between the Milky Way and Sagittarius may have influenced the environment in which successive generations of stars were born.

Some studies have noted an intriguing chronological relationship between proposed Sagittarius passages and episodes of enhanced star formation within the Milky Way.

Such connections must be treated with scientific caution. Galactic star formation is influenced by numerous processes, and correlation alone is not sufficient to establish a simple one-to-one cause.

Nevertheless, the possibility is profoundly interesting.

A dwarf galaxy being destroyed by the Milky Way may, at the same time, have helped stir the gas from which new Milky Way stars were subsequently formed.

Cosmic history is rarely a straightforward tale of predator and prey.

9. The Dark Matter Question Hidden Inside the Sagittarius Stream

The Sagittarius stream has another importance which is seldom discussed outside specialist astronomy.

It may help astronomers investigate the small-scale structure of dark matter.

According to prevailing cosmological models, galaxies such as the Milky Way are surrounded by extensive dark-matter haloes.

These haloes may also contain smaller concentrations or subhaloes.

Because dark matter does not emit ordinary light, such structures can be extraordinarily difficult to detect directly.

A stellar stream, however, may act as a sensitive gravitational probe.

If a sufficiently massive unseen object passes near a stream, it may alter the motions of stars or create variations in the stream's density.

One might therefore search for irregularities within stellar streams as possible evidence of gravitational encounters with otherwise invisible structures.

The idea is subtle but powerful.

We may be unable to see the intruder, yet we may observe its footprints in the disturbed motions of stars.

This is rather like inferring the passage of an unseen ship by examining the wake left upon the water.

The Sagittarius stream is particularly valuable because it is extensive, massive and dynamically rich.

Its detailed structure may therefore help astronomers refine their understanding not merely of Sagittarius itself, but of the invisible architecture surrounding the Milky Way.

10. A Chemical Fingerprint Across the Galaxy

Stars carry chemical information about the environments in which they formed.

A star's elemental composition can therefore serve as a kind of historical signature.

This field is sometimes described as chemical tagging or, more broadly, Galactic archaeology.

The Sagittarius system contains stars with a variety of ages and chemical compositions. As these stars are dispersed along the tidal stream, they carry evidence of the dwarf galaxy's internal history.

Recent work using large Gaia-based stellar samples has examined chemical variations across the Sagittarius stream.

Such measurements are valuable because they can help astronomers distinguish Sagittarius stars from unrelated Milky Way populations.

They may also reveal which portions of the original dwarf galaxy were stripped during different periods.

This leads to a remarkable possibility.

The outer regions of a disrupted galaxy may have been removed first, while stars from more tightly bound regions remained longer within the surviving remnant.

The resulting stream may therefore contain a chronological and chemical record of the galaxy's gradual disassembly.

One could say that Sagittarius is being scattered across the heavens, but not entirely silenced.

Its stars continue to tell its story.

11. Why Individual Stars Rarely Collide

When people hear that one galaxy is passing through another, the natural assumption is that stars must collide in enormous numbers.

Fortunately, the Universe is much emptier than it appears in illustrations.

Even within galaxies, the distances between stars are immense.

During a galactic encounter, stars generally pass one another without direct physical collision.

The principal interaction is gravitational.

Galaxies may therefore merge and profoundly alter one another while the overwhelming majority of their individual stars never strike another star.

This is one reason why the term “galactic collision” can be misleading if interpreted too literally.

The galaxies collide as gravitational systems.

Their stars, gas and dark matter respond to changing gravitational fields.

Gas clouds may interact far more dramatically because gas is diffuse and can experience shocks and compression.

Stars, by contrast, usually continue through the encounter as individual objects following altered orbits.

Thus, Sagittarius is not being destroyed because its stars are crashing into Milky Way stars.

It is being dismantled because the Milky Way's gravitational field is gradually pulling its stellar population apart.

12. Is the Milky Way a “Cannibal Galaxy”?

In a loose popular sense, yes.

In a scientific sense, the term should be used carefully.

Galaxies do not consume one another as biological organisms consume prey. They merge through gravitational interaction and accretion.

Nevertheless, the Milky Way has unquestionably grown through the incorporation of smaller systems.

Modern observations reveal that the Galactic halo contains evidence of ancient mergers and accreted stellar populations.

The Sagittarius interaction is especially valuable because it represents a relatively recent and still continuing chapter in this long process.

We are therefore not merely studying a fossil from the Milky Way's distant youth.

We are observing a process that remains dynamically active.

Indeed, recent research into the Milky Way's earliest mergers has further strengthened the broader picture of our Galaxy as an object assembled through repeated interactions across cosmic history.

The Milky Way, therefore, is not the finished article it may appear to be when viewed as a serene band of light across the night sky.

It is a historical construction site.

13. The Fate of Sagittarius: What Can We Say With Confidence?

The broad conclusion is clear.

Sagittarius is undergoing continuing tidal disruption.

Its stellar material has already been distributed into vast streams around the Milky Way, and the surviving central remnant is severely affected by the Galaxy's gravitational forces.

Models generally indicate that the remnant will continue to lose coherence and material.

However, one should avoid presenting the exact future as though it were known to the nearest astronomical appointment.

The evolution of Sagittarius depends upon several complicated factors:

its remaining mass;
its distribution of dark matter;
the detailed shape of its orbit;
the gravitational structure of the Milky Way;
past orbital evolution;
and perturbations from other massive components of the Galactic system.

Consequently, statements about precisely when Sagittarius will cease to exist as a recognisable remnant should be understood as model-dependent estimates rather than a date engraved upon the celestial calendar.

The eventual direction of the story, however, is not seriously in doubt.

Sagittarius is becoming progressively integrated into the Milky Way's larger gravitational system.

Its identity as a separate galaxy is being eroded.

14. A Billion-Year Story in One Diagram

Conceptual illustration: The diagram represents the broad evolutionary sequence rather than a precise chronological scale.

15. The Most Extraordinary Aspect: We Are Inside the Larger Galaxy

There is a philosophical peculiarity in the Sagittarius story.

We are not observing this interaction from some distant galaxy.

We live inside the larger participant.

The Milky Way surrounds us.

Its disc, halo and gravitational field form the environment through which the Solar System travels.

Somewhere within this immense structure are stars that originated elsewhere and were later incorporated through ancient mergers.

The Sun itself was born within the Milky Way, but the Galaxy in which it formed had already been shaped by earlier encounters.

It is therefore reasonable to regard the Milky Way as a composite historical object.

Some of its stars formed within its original progenitor.

Others were acquired from smaller galaxies.

The boundaries between “our Galaxy” and “another Galaxy” can eventually become blurred by the slow action of gravity.

Given sufficient time, a galaxy can cease to exist as a separate entity while its stars continue their journeys indefinitely.

That may ultimately be the fate of Sagittarius.

16. What the Sagittarius Dwarf Teaches Us Beyond the Textbook

The story of Sagittarius offers several lessons that are often absent from elementary discussions of galaxies.

1. Galactic destruction can preserve information

It might appear that the destruction of a galaxy would erase its history. In reality, tidal disruption can distribute that history across space. The resulting stellar streams preserve positions, motions and chemical signatures that may reveal the structure of the original system.

2. A smaller galaxy can alter a larger one

Sagittarius is being disrupted, but its repeated gravitational encounters have also disturbed the Milky Way's disc. In astronomy, size does not imply complete immunity from influence.

3. Stellar streams are laboratories for invisible matter

Streams respond to the gravitational field through which they travel. Their shapes and density variations may therefore provide clues about the Milky Way's dark-matter halo and possible substructure within it.

4. Galactic archaeology is becoming increasingly dynamic

Astronomers no longer reconstruct Galactic history solely from where stars are located. Gaia and spectroscopic surveys increasingly allow researchers to examine where stars are, how they move and what chemical history they carry.

5. The Milky Way is still evolving

Our Galaxy is not a completed object preserved in cosmic aspic. It remains dynamically active, influenced by satellite galaxies and continuing gravitational evolution.

17. A Quiet Lesson in Cosmic Impermanence

There is something almost poetic about the Sagittarius Dwarf Galaxy.

A galaxy may appear to us as a permanent celestial kingdom, yet even such a vast structure can lose its identity.

Its stars need not perish.

They will continue to shine.

What disappears is the gravitational arrangement that once bound them together as a distinct galaxy.

Over time, Sagittarius may become increasingly difficult to recognise as a separate astronomical entity.

Yet its former existence will remain written into the Milky Way.

Its stars will continue along their orbits.

Its chemical signatures will remain measurable.

Its gravitational encounters may remain encoded in the motions of the Galactic disc.

Its history may continue to be reconstructed long after its surviving core has disappeared as a recognisable structure.

In astronomy, therefore, disappearance does not necessarily mean oblivion.

The Universe has an excellent memory.

Conclusion: The Milky Way's Unfinished Feast

The ongoing disruption of the Sagittarius Dwarf Galaxy is among the most remarkable examples of cosmic evolution available for direct study within our own Galactic neighbourhood.

The Milky Way's gravitational field has progressively stripped Sagittarius of stars and stretched its material into immense tidal streams.

These streams now provide astronomers with more than a dramatic illustration of galactic cannibalism. They offer a means of studying the Milky Way's gravitational field, its dark-matter halo and the complicated history of Galactic assembly.

Meanwhile, Sagittarius itself has not remained an entirely passive victim.

Its repeated passages may have disturbed the Milky Way's disc, contributed to dynamical ripples and possibly influenced episodes of star formation.

The relationship between the two galaxies is therefore not merely one of destruction.

It is an interaction.

A smaller galaxy is gradually losing its separate identity, while simultaneously leaving a measurable imprint upon the larger Galaxy that is absorbing it.

Perhaps that is the most compelling lesson of all.

The Milky Way is not simply eating Sagittarius.

Sagittarius is becoming part of the Milky Way's memory.

And through modern astronomy, particularly the extraordinary cartographic work of Gaia and complementary observations from other observatories, humanity is learning how to read that memory.

Did You Know?

★ The Sagittarius stream is larger than the surviving galaxy.
Much of the original Sagittarius system has already been distributed into stellar streams extending across a vast region of the sky.

★ We can identify a lost galaxy through stellar motion.
Stars separated by enormous distances may still reveal a common origin because they share related patterns of motion through the Galaxy.

★ Galactic mergers rarely involve direct stellar collisions.
The immense distances between stars mean that gravitational disruption is far more important than physical collisions between individual stars.

★ Sagittarius may have shaken the Milky Way.
Its repeated encounters are associated with disturbances in the Galactic disc and have been investigated as a possible influence upon episodes of enhanced star formation.

★ Stellar streams may reveal invisible dark-matter structures.
Irregularities in streams can potentially record gravitational encounters with objects that cannot themselves be seen.

Glossary

Accretion: The gradual accumulation of matter by a larger astronomical object or system.
Dark Matter: Matter inferred primarily through its gravitational influence but not directly observed through ordinary electromagnetic radiation.
Galactic Archaeology: The reconstruction of a galaxy's history through the positions, motions, ages and chemical compositions of its stars.
Galactic Halo: An extended region surrounding a galaxy that contains stars, globular clusters and a substantial dark-matter component.
Gravitational Potential: A mathematical description of the gravitational environment governing the motion of objects within a system.
Hierarchical Galaxy Formation: The cosmological idea that larger galaxies grow partly through the merger and accretion of smaller structures.
Parallax: The apparent displacement of a nearby object against distant background objects when observed from different positions.
Phase Space: A description of an object's position and motion, often incorporating spatial coordinates and velocity components.
Proper Motion: The apparent angular movement of a star across the sky as observed over time.
Sagittarius Dwarf Spheroidal Galaxy: A satellite galaxy of the Milky Way undergoing significant tidal disruption.
Stellar Stream: An extended structure of stars sharing a common origin and orbital history, often produced when a dwarf galaxy or star cluster is gravitationally disrupted.
Tidal Force: A differential gravitational force arising because gravity acts with different strength across an extended object.

References

European Space Agency (ESA), Gaia: The Sagittarius Dwarf Galaxy and the Milky Way.
European Space Agency (ESA), Five Fascinating Gaia Revelations About the Milky Way.
NASA Astronomy Picture of the Day, The Sagittarius Dwarf Tidal Stream.
NASA Science, Hubble Solves Merger Mystery From the Milky Way's Early Years, 2026.
Antoja, T. and collaborators, studies of dynamical disturbances and phase-space structure in the Milky Way revealed through Gaia observations.
Ruiz-Lara, T. and collaborators, The Recurrent Impact of the Sagittarius Dwarf on the Star Formation History of the Milky Way, Nature Astronomy.
Abonaca, A. and collaborators, Stellar Streams in the Gaia Era, New Astronomy Reviews.
Studies of the structure, kinematics and tidal disruption of the Sagittarius Dwarf Spheroidal Galaxy using Gaia data and spectroscopic surveys.

Copyright and Usage

This article is an original work researched, written, edited and compiled by Dhinakar Rajaram for public understanding and informed scientific discussion.

The structure, narrative, explanations, interpretations and presentation contained in this essay constitute the author's intellectual work. Scientific facts and concepts have been independently synthesised from publicly available scientific literature, institutional material and established astronomical knowledge.

Readers may share the original link to this article for non-commercial educational discussion. Reproduction of this article in substantial part, republication, commercial use, alteration or presentation as another person's original work requires prior permission from the author.

The scientific understanding of astronomy continues to evolve. Numerical estimates and theoretical interpretations may be refined as new observations, surveys and models become available.

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Sunday, 6 September 2026