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NASA faced with massive budget cuts in White House proposal

NASA could see a 20 percent cut to its overall 2026 budget, with funding for its science division slashed in half, if a preliminary budget proposal from the White House is enacted. The cuts would, among other impacts, cancel several missions and shut down NASA’s Goddard Space Flight Center. The proposed cuts were laid outContinue reading "NASA faced with massive budget cuts in White House proposal"

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C/2025 F2 (SWAN): A new comet is in the spring sky

In late March, three amateur astronomers discovered Comet C/2025 F2 (SWAN). Immediately, predictions began appearing online stating the brightness this object might reach. But, as comet discoverer David Levy says, “Comets are like cats. They have tails and do what they want.”  In other words, don’t bet the house that current predictions will come true.Continue reading "C/2025 F2 (SWAN): A new comet is in the spring sky"

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The Sky This Week from April 11 to 18: The April Full Pink Moon shines

Sky This Week is brought to you in part by Celestron. Friday, April 11An hour after sunset, the bright planet Jupiter stands out in eastern Taurus, forming a V with the two tips of the Bull’s horns, Zeta (ζ) Tauri and Gamma (γ) Aurigae. Below Jupiter shines Aldebaran, the Bull’s alpha star, a magnitude 0.9Continue reading "The Sky This Week from April 11 to 18: The April Full Pink Moon shines"

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Amateur astronomy industry grapples with tariff chaos

The telescope industry in the U.S. has been thrown into chaos as a result of the Trump administration’s escalating trade conflict with China, as manufacturers contemplate price hikes and worry about the possibility of slowing demand. In the latest round of tariffs, U.S. President Donald Trump announced April 9 that duties on goods imported fromContinue reading "Amateur astronomy industry grapples with tariff chaos"

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Come with Astronomy associate editor Michael Bakich to Egypt

I’m leading another eclipse trip. No surprise there. I’ve traveled to observe 16 total solar eclipses, and on all but two of them I was the official astronomer. But this one’s special, even for me.  First, it boasts the longest totality — 6 minutes 23 seconds — that anyone alive will be able to witness.Continue reading "Come with Astronomy associate editor Michael Bakich to Egypt"

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A fledgling SWAN

Chris Schur from Payson, Arizona Comet C/2025 F2 (SWAN), discovered March. 29 by amateur astronomers in public imagery taken by the Solar Wind Anisotropies (SWAN) camera on ESA’s Solar and Heliospheric Observer (SOHO) spacecraft, has reached magnitude 7.5. This imager caught the comet on April 8 in the morning sky with an 8-inch RASA scopeContinue reading "A fledgling SWAN"

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How you can observe impacts on Jupiter

Lucky is the word I’d use for any telescopic observers who got to see one of the most stunning spectacles in nature when Comet Shoemaker-Levy 9 impacted Jupiter in July 1994. The collision left inky scars in the planet’s atmosphere that persisted for months, with the largest welts visible in even the smallest of telescopes.Continue reading "How you can observe impacts on Jupiter"

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Three new planets found around Barnard’s Star

As of 2025, astronomers have identified at least 14 stars within 10 light-years of the Sun. After the Alpha Centauri system, the next closest is Barnard’s Star, a solo red dwarf roughly 6 light-years away. And thanks to new observations, we now know that Barnard’s Star is orbited by four small, rocky exoplanets. But it’sContinue reading "Three new planets found around Barnard’s Star"

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This Week in Astronomy with Dave Eicher: The April Lyrid Meteor Shower

In this episode, Astronomy magazine Editor Dave Eicher invites you to head out and view the first major meteor shower of the spring, the Lyrids. Because more than one meteor shower originates from the constellation Lyra, these are the April Lyrids. This shower is visible from April 15 to April 29, with the peak coming on AprilContinue reading "This Week in Astronomy with Dave Eicher: The April Lyrid Meteor Shower"

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Mystery ‘interstellar icy objects’ are carrying the seeds of life

In the century or so since Edwin Hubble discovered that the Milky Way is just one of countless galaxies in the universe, our understanding of our home galaxy has grown in leaps and bounds. But as recent research into a new type of cosmic object shows, there’s still plenty left to learn. Astronomers found twoContinue reading "Mystery ‘interstellar icy objects’ are carrying the seeds of life"

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The summer Milky Way returns

Gianni Tumino from Ragusa, Italy Evening views of the Milky Way’s central regions return to the Northern Hemisphere, as seen in this shot taken from Punta Castellazzo on the island of Sicily, Italy. To image the sky, the imager used a Canon EOS Ra and 28mm lens at f/3.2 with a dual-band filter to captureContinue reading "The summer Milky Way returns"

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SpaceX, Blue Origin, ULA win Space Force contracts worth up to $13.7B

Launch providers SpaceX, Blue Origin, and United Launch Alliance — a joint venture between Boeing and Lockheed Martin Space — on Friday snapped up billions of dollars in national security launch contracts. Space Systems Command, the branch of Space Force responsible for development, acquisition, launch, and logistics, estimated the value of the National Security Space Launch (NSSL)Continue reading "SpaceX, Blue Origin, ULA win Space Force contracts worth up to $13.7B"

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ESO report shows energy plant would cause ‘devastating and irreversible’ impact

A new study by the European Southern Observatory (ESO) contradicts corporate claims that a proposed hydrogen fuel facility would not harm observatories in Chile. Earlier this year, ESO alerted the astronomy community that its facilities at Paranal — with some of the world’s darkest skies — were threatened by the plans to build a 7,400-acreContinue reading "ESO report shows energy plant would cause ‘devastating and irreversible’ impact"

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The best new astronomy products we saw at NEAF 2025

The annual Northeast Astronomy Forum (NEAF) was held over the weekend of April 5 and 6 at Rockland Community College in Suffern, New York. Organized by the Rockland Astronomy Club, NEAF is one of the world’s premier annual astronomy expos. It brings together amateur astronomers, professionals, and industry leaders for a weekend of discovery andContinue reading "The best new astronomy products we saw at NEAF 2025"

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Was there ever a planet between Mars and Jupiter? 

Is there evidence of a planet ever existing between Mars and Jupiter? MarkSmithtown, New York This splendid question gives us an opportunity to distinguish between what we know and what we believe might be true. First, we know that myriad small bodies orbit the Sun between Mars and Jupiter. These objects are the asteroids that comprise the mainContinue reading "Was there ever a planet between Mars and Jupiter? "

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Review: Astronomy tests Vaonis’ Hestia telescope for your smartphone

The new Hestia telescope by Vaonis is the third of the company’s innovative instruments I have reviewed, and once again, I’m impressed. Vaonis named their creation for the Greek goddess of the hearth and home, and released it after a successful 2023 Kickstarter campaign which raised $4.1 million in just a month. The Hestia isContinue reading "Review: Astronomy tests Vaonis’ Hestia telescope for your smartphone"

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How Project Gemini changed spaceflight

Sixty years ago, a fleet of sleek little spaceships paved the way for America to land a man on the Moon. Project Gemini was a series of two-man, Earth-orbital missions that pioneered rendezvous, docking, and maneuvering in-space, as well as spacewalking — all of which had to be perfected before there was any chance ofContinue reading "How Project Gemini changed spaceflight"

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Horns of the Sun

Fabrizio Melandri from Voltana, Italy The partial solar eclipse of March 29, 2025, gave viewers along the U.S. Eastern Seaboard a view of “devil’s horns” — the horns of a partially eclipsed Sun emerging from the horizon at sunrise. This photographer captured this phenomenon from Monticello, Maine, with a 4-inch f/7 refractor and Nikon DSLR.

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Fram2 astronauts splash down after historic polar spaceflight

The first astronaut crew to fly directly over Earth’s poles splashed down safely on Friday after nearly four days on orbit. Civilian astronauts Chun Wang, Jannicke Mikkelsen, Rabea Rogge, and Eric Phillips — the international crew of SpaceX’s private Fram2 mission — landed around 12:19 p.m. EDT and exited their SpaceX Dragon capsule without assistance, allowing researchers to study how theContinue reading "Fram2 astronauts splash down after historic polar spaceflight"

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HoverAir X1 PRO drone review

The HoverAir X1 PRO is one of two new ZeroZero Robotics selfie drone models and is the more affordable option of the two with 4K video capture with a host of optional accessories available.

© James Abbott

Curiosity discovers largest organic molecules yet on Mars

The Mars Curiosity rover has found the largest organic molecules yet on the Red Planet. Organic molecules are the building blocks of life, although they can also be produced by geological processes. While there’s currently no way to prove whether these particular molecules were formed from processes associated with life, their very discovery shows thatContinue reading "Curiosity discovers largest organic molecules yet on Mars"

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The Sky This Week from April 4 to 11: Catch your last views of Uranus

Sky This Week is brought to you in part by Celestron. Friday, April 4This evening, the roughly half-illuminated face of the Moon hangs in Gemini, high in the south an hour after sunset. First Quarter Moon occurs at 10:15 P.M. EDT. The two brightest stars in Gemini are Castor (magnitude 1.6) and Pollux (magnitude 1.2).Continue reading "The Sky This Week from April 4 to 11: Catch your last views of Uranus"

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Megaroc: The British manned space program that almost was

As World War II drew to a close, the Allies were eager to get their hands on one of the most technologically amazing yet terrifying weapons in Nazi Germany’s armamentarium: the V-2 rocket. A long-range, liquid-fueled supersonic guided missile, the V-2 could carry a 2,000-pound (910 kilograms) warhead a staggering 200 miles (320 kilometers) fromContinue reading "Megaroc: The British manned space program that almost was"

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What's the difference between a young exoplanet and an old one?

A new study compares young and old exoplanets to uncover how worlds shrink, migrate and evolve over time — offering insights into long-standing astronomical mysteries like the "hot Neptune desert" and the "radius valley."

© NASA/Ames/JPL-Caltech

Cosmic wingspan

Andrei Pleskatsevich, taken from Minsk, Belarus The Seagull Nebula is a region of nebulosity lying on the border between constellations Monoceros and Canis Major; the emission nebula forming the bird’s “head” carries the catalog designation IC 2177. The imager used a 3-inch f/4.5 scope and one-shot color camera to take 10 hours of exposure.

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Space miso is nuttier than Earth miso — but it's still miso

Scientists have successfully fermented miso aboard the International Space Station, marking the first deliberate food fermentation in space that may open up new culinary possibilities for astronauts on long-term missions.

© Maggie Coblentz

Spring for new astronomy products this month

Sky watchers The University of Arizona PressTucson, AZ Star Gazers: Finding Joy in the Night Sky, by prolific astronomy writer David H. Levy, is a collection of personal essays celebrating amateur and professional astronomy. Bringing together his decades of sky-watching experience, this 172-page book gives readers insight into Levy’s thoughts on James Webb Space Telescope,Continue reading "Spring for new astronomy products this month"

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FAA concludes Blue Origin, SpaceX January ‘mishap’ investigations

The Federal Aviation Administration has completed its investigations looking into “mishaps” that occurred during Blue Origin’s New Glenn rocket launch and SpaceX’s Starship Flight 7 in January. On Jan. 16, Blue Origin’s New Glenn-1 reached orbit on its debut flight. While the launch was successful, the rocket lost its lower stage during its descent. Later thatContinue reading "FAA concludes Blue Origin, SpaceX January ‘mishap’ investigations"

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Debut flight of Isar Aerospace Spectrum rocket ends in explosion

he first commercially built rocket to lift off from continental Europe came tumbling back to Earth within seconds. But its manufacturer considers the mission a success. The test flight, “Going Full Spectrum,” was the debut launch of Norwegian company Isar Aerospace’s Spectrum, a two-stage orbital launch vehicle designed to compete with SpaceX’s workhorse Falcon 9Continue reading "Debut flight of Isar Aerospace Spectrum rocket ends in explosion"

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Earth as a planet

From the editor: As the extraordinary pace of astronomical discovery carries on, we increasingly see that the stuff of life is spread throughout the cosmos. Life, even complex life, must be common out there. We know of several hundred billion stars in our galaxy, at least 100 billion galaxies, and planets around most of theContinue reading "Earth as a planet"

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Solving the climate equation

My childhood fascination with the night sky led me to study astronomy and physics at university. By my second year, I was operating the telescope atop the physics building, tracking celestial objects — just like astronomy student Kate Dibiasky in the disaster movie Don’t Look Up.I never imagined I’d also soon find myself alerting othersContinue reading "Solving the climate equation"

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How to build climate solutions: An interview with Tony Fadell

In many ways, Tony Fadell built the digital world we live in. At the turn of the millennium, his efforts to build a pocket-sized, hard-disk-based device that could hold 1,000 songs in MP3 format caught the attention of Apple. Within months, he had been hired by the firm, and less than a year after hisContinue reading "How to build climate solutions: An interview with Tony Fadell"

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SpaceX’s Fram2 mission will aim for the poles

Next week, a crew of private astronauts is expected to go where no one has gone before. Chun Wang, the crypto entrepreneur who purchased the Fram2 mission from SpaceX in August, announced Friday that the three-to-five-day sojourn — the first human spaceflight to fly directly over the Earth’s poles — is scheduled to launch fromContinue reading "SpaceX’s Fram2 mission will aim for the poles"

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German firm eyes Thursday for Europe’s first commercial orbital launch

After a scrubbed test flight on Monday, a German spaceflight company has determined its next opportunity to launch the first commercial orbital launch vehicle from mainland Europe. Munich-based Isar Aerospace postponed the debut launch of its Spectrum rocket, citing unfavorable winds at Norway’s Andøya Spaceport. On Tuesday, Isar said it will now target Thursday atContinue reading "German firm eyes Thursday for Europe’s first commercial orbital launch"

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This dead star is still sending us radio signals

Astronomers have finally identified the source of mysterious radio waves from deep space, tracing the signals back to an unusual stellar pair locked in a swift orbit, flashing out their location for the universe to hear. In research published March 12 in Nature Astronomy, a team of astrophysicists finally found the source of strange, minute-longContinue reading "This dead star is still sending us radio signals"

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Ghost rivers, hidden lakes: The long search for water on Mars

The quest to send humans to Mars is on: US President Donald Trump talked about it in his inauguration speech this year. Such an epic endeavor could help to answer fundamental questions about the Red Planet, including the biggest question of all: Did Mars once host life — and does it still? Central to thoseContinue reading "Ghost rivers, hidden lakes: The long search for water on Mars"

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Bathed in blue

Greg Polanski from Kanata, Ontario, Canada The ever-popular Rosette Nebula (NGC 2237–9/46) lies 10° east of Betelgeuse and is an impressive telescopic sight. Deep imaging reveals the line of dark Bok globules — small dense clouds where baby stars are forming — that appear to lie suspended within the nebula. The imager took 12⅓ hoursContinue reading "Bathed in blue"

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How do neutrino telescopes work?

To detect neutrinos, scientists use vast observatories located underground, shielded from cosmic ray interference. These detectors rely on Cherenkov radiation, a bluish light produced when high-speed muons, created by rare neutrino collisions, travel faster than light through water or ice. Photomultiplier tubes amplify this light, allowing astronomers to trace the neutrino’s path and energy.

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Rare moonbow shines below total lunar eclipse in stunning photo: 'This is definitely the first time I've tried something like this, but will not be the last'

"The respective sizes of the two arcs also create a great symbolic representation of the difference in scale between what we experience and deal with as humans on Earth and the vastness and grandeur of the scale of space and our closest neighbor"

© Billy Buchanan, Narcoleptic Nightscapes

Our solar system is not as unusual as we thought

Astronomers have discovered more than 300 exoplanetary systems that have three or more known planets. Most of these planets are about the same size and spaced close together, earning them the moniker “peas in a pod.” They also orbit near their stars, in many cases closer than Mercury is to the Sun.  Our solar system,Continue reading "Our solar system is not as unusual as we thought"

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Will Sirius B explode as a type Ia supernova?

Could the nearby star Sirius B explode as a type Ia supernova, like some other white dwarf stars in binary star systems have? Bruce MasonEncinitas, California A type Ia supernova occurs when a white dwarf — the cooling remnant of an aging star — draws hydrogen from a companion sun. When the dwarf reaches 1.4Continue reading "Will Sirius B explode as a type Ia supernova?"

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This Week in Astronomy with Dave Eicher: A Solar Eclipse

In this episode, Astronomy magazine Editor Dave Eicher invites you to view an unusual event: a partial eclipse of the Sun. Depending on where you are, you might see the Moon cover up to 90 percent of the bright solar disk. Remember, however, even 10 percent of the Sun is dangerous to look at, so wear approvedContinue reading "This Week in Astronomy with Dave Eicher: A Solar Eclipse"

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Our near galactic neighbor might have a supermassive black hole

The Large Magellanic Cloud (LMC) is one of the Milky Way’s closest neighbors. It’s a small, irregular galaxy that orbits the Milky Way, and is an easy naked-eye object from the Southern Hemisphere. As one of the only galaxies outside our own where telescopes can resolve individual stars and small scale structures, astronomers love toContinue reading "Our near galactic neighbor might have a supermassive black hole"

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Stellar nursery sparkles at the edge of our galaxy in gorgeous Hubble Telescope image

The emission nebula, known as Sh2-284, is an immense region of gas and dust that fuels new star formation. It lacks elements heavier than hydrogen and helium, much like the environment of the early universe.

© NASA, ESA, and M. Andersen (European Southern Observatory - Germany); Processing: Gladys Kober (NASA/Catholic University of America)

The Sky This Week from March 21 to 28: Galilean moon action

Sky This Week is brought to you in part by Celestron. Friday, March 21By 10 P.M. local daylight time, the constellation Canes Venatici the Hunting Dogs is some 45° high in the east. Nestled under the curve of the Big Dipper’s handle, this seemingly innocuous star pattern hosts several popular deep-sky objects.  One of thoseContinue reading "The Sky This Week from March 21 to 28: Galilean moon action"

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یافتن کهکشان‌های کوتوله‌ی خاموش‌ در خلوت‌ترین نقاط کیهان

چه چیزی باعث از بین رفتن توان ستاره‌زایی در کهکشان‌های کم‌جرم یا کوتوله می‌شود؟ این سوالی است که منجمان مدت‌ها معتقد بودند پاسخ دقیق به آن را یافته‌اند، اما نتایج جدید نشان می‌دهد که ما هنوز از تصویری دقیق و واقع‌بینانه دور هستیم.

کهکشان‌های کوتوله، که جرم ستاره‌ای آن‌ها حدود یک تا دو میلیارد برابر جرم خورشید یا کم‌تر است، از رایج‌ترین انواع کهکشان‌ها در کیهان محسوب می‌شوند. به عنوان مثال، در گروه محلی۱ بیش از ۶۰ کهکشان کوتوله وجود دارد و این تعداد، با بهتر شدن حساسیت تلسکوپ‌ها، روز به روز در حال افزایش است. داده‌های رصدی وجود تعداد زیادی از کهکشان‌های کوتوله‌ی قرمز و خاموش۲ در مراکز پرتراکم کیهان مانند مرکز گروه‌ها و خوشه‌های کیهانی را تایید می‌کند، در حالی‌که کهکشان‌هایی که در محیط‌های خلوت‌تر (مانند اطراف گروه محلی یا در محیط‌هایی خارج از خوشه‌ها) رصد شده‌اند، غالبا حاوی گاز و در حال ستاره‌زایی هستند. بر اساس این مشاهدات این باور کلی به وجود آمده است که محیط تنها عامل خاموش‌شدن ستاره‌زایی در کهکشان‌های کوتوله است.

زمانی که یک کهکشان با سرعت زیاد درون محیط متراکم و داغ گاز خوشه‌ای حرکت می‌کند، تحت نیرویی به نام فشار ترمزی۳ قرار می گیرد. این نیرو در اثر برخورد و حرکت کهکشان در میان گاز میان خوشه‌ای، بر آن اعمال می‌شود و می‌تواند گاز سرد درون کهکشان را از آن خارج کند. هر چقدر جرم کهکشان بیش‌تر باشد، چاه پتانسیل عمیق‌تری خواهد داشت و خارج کردن گاز سرد از آن سخت‌تر خواهد بود. چاه پتانسیل کم‌عمق کهکشان‌های کوتوله، آن‌ها را به یک قربانی بسیار ساده برای محیط‌های متراکم و شلوغ کیهان تبدیل می‌کند. مثال بارز این پدیده، کهکشان کوتوله‌ی مسیه ۱۱۰ در فاصله ۲/۷۱ میلیون سال نوری از خورشید است. این کهکشان کوتوله حدود چند میلیارد سال قبل، یعنی درست زمانی که وارد خوشه‌ی محلی می‌شده‌است، تمامی گاز خود را از دست داده‌است. مسیه ۱۱۰ امروز یک کهکشان کوتوله‌ی خاموش است که با نور قرمز و توزیع نوری کاملا یکنواخت، در تصاویر نجومی خودنمایی می‌کند.

چرا درک بهتر فرایند خاموش‌شدن کهکشان‌های کوتوله تا این اندازه اهمیت دارد؟ پاسخ ساده به این سوال این است که هر آن‌چه که بتواند ستاره‌زایی را در کهکشان‌های کوتوله متوقف کند، می‌تواند (با نسبت‌های متغیر) سبب خاموش‌شدن کهکشان‌های بزرگ‌تر نیز شود. در واقع، مطالعه‌ی آغاز و پایان ستاره‌زایی در این کهکشان‌ها می‌تواند یک تصویر دقیق از تمامی فرایندهایی که ستاره‌زایی در کهکشان‌ها را مدیریت می‌کند، ارائه دهد. از طرف دیگر، بر اساس مدل استاندارد کیهان‌شناسی Lambda-CDM، این کهکشان‌های کوتوله (یا نمونه‌های هم‌جرم آن‌ها) بودند که ابتدا در عالم شکل گرفتند و سپس، با ادغام‌شدن، کهکشان‌های بزرگ‌تر را شکل دادند. بنابراین، درک بهتر این کهکشان‌ها در واقع درک بهتر آجرهایی است که عالم امروزی را بنا کرده‌اند.

در جستجوی کوتوله‌های خاموش و منزوی!

اگر محیط تنها عامل خاموش‌شدن ستاره‌زایی در کهکشان‌های کوتوله باشد، بنابراین هیچ کهکشان کوتوله‌ی خاموشی نباید در کم‌تراکم‌ترین نقاط کیهان، یعنی تهی‌جاها۴ و رشته‌های کیهانی۵ وجود داشته باشد. تهی‌جاهای کیهانی مناطق وسیعی از کیهان، با ابعاد حدودی ۱۰ تا ۱۰۰ مگاپارسک، هستند که در مقایسه با خوشه‌های کهکشانی، چگالی ماده‌ی بسیار کم‌تری دارند. رشته‌های کیهانی در مرز میان تهی‌جاها قرار گرفته‌اند. برای راستی‌آزمایی این فرضیه، ما به سراغ ۴۲ تهی‌جای کیهانی در بازه‌ی انتقال به سرخ ۰/۰۰۵ تا ۰/۰۵، که کاتالوگ آن‌ها توسط تیم CAVITY جمع‌آوری شده‌است، رفته‌ایم. برای بررسی کوتوله‌ها در رشته‌های کیهانی نیز از کاتالوگ کهکشان‌های رشته‌ای Dominguez-Gomez et al. 2023 استفاده کردیم. هدف ما پیداکردن تنهاترین کوتوله‌ها در کم‌تراکم‌ترین نقاط کیهان بود. بنابراین، کهکشان‌های کوتوله‌ای را در این تهی‌جاها و رشته‌ها انتخاب کردیم که هیچ کهکشان همسایه‌ای، تا فاصله‌ی ۱ مگاپارسکی، از آن‌ها حضور نداشته باشد. دلیل این انتخاب، مطالعاتی هستند که ثابت کرده‌اند یکی از علت‌های خاموشی در کهکشان‌های کوتوله، نزدیکی یا همسایگی با کهکشان‌های دیگر است. سپس در این مطالعه به بررسی تاریخچه‌ی ستاره‌زایی در این کهکشان‌ها با کمک تکنیک‌های طیف‌سنجی، با استفاده از داده‌های طیفی Sloan Digital Sky Survey پرداختیم. طیف‌سنجی یک ابزاری کلیدی و دقیق برای بررسی کهکشان‌هاست و به ما کمک می‌کند تا تخمینی از سن، درصد فراوانی آهن (عناصر سنگین‌تر از هلیوم) و روند ستاره‌زایی در کهکشان ‌داشته باشیم.

شکل ۱. گروهی کمیاب از کهکشان‌های کوتوله‌ی خاموش و منزوی در تهی‌جاها و رشته های کیهانی.

این جستجو سبب شد تا ما گروهی کمیاب از کهکشان‌های کوتوله‌ی پرجرم  و  خاموش را پیدا کنیم که در تنهاترین و کم‌چگال‌ترین نقاط کیهان حضور دارند. ستاره‌زایی در این کهکشان‌ها بیش از ۲ میلیارد سال پیش متوقف شده‌است و هیچ گازی در این کهکشان‌ها وجود ندارد. این کهکشان‌ها از نظر برخی خصوصیات مانند اندازه و جرم، تفاوتی با سایر کهکشان‌های کوتوله‌ی خاموش در خوشه‌ها ندارند، اما وجه مشترک تمامی آن‌ها، میزبانی از خوشه‌های ستاره‌ای هسته‌ای۶ است. خوشه‌های ستاره‌ای هسته‌ای، مجموعه‌ای فشرده از ستارگان هستند که در مرکز بسیاری از کهکشان‌ها، از جمله کهکشان‌های کوتوله و حتی در راه شیری پیدا می‌شوند. این خوشه‌ها از لحاظ جرم و چگالی، درخشان‌ترین و متراکم‌ترین خوشه‌های ستاره‌ای در کهکشان میزبان خود محسوب می‌شوند.

در شکل ۲، ما تاریخچه‌ی ستاره‌زایی این کهکشان‌ها را با نمونه‌های مشابه (از نظر جرم) در خوشه‌های بزرگ کیهانی مقایسه کردیم. آن‌چه که قابل توجه است، شباهت میزان ستاره‌زایی در برخی از این کهکشان‌های کوتوله‌ی خاموش‌ در تهی‌جاها و رشته‌ها با گروهی از کهکشان‌های کوتوله‌ است که امروزه در مرکز خوشه‌های کیهانی قرار دارند. کهکشانی که امروز در مرکز یک خوشه‌ی کیهانی قرار داشته باشد، بیش از ۵ میلیارد سال را در آن خوشه زندگی کرده‌است و این به معنای قرارگرفتن در معرض تمامی محرک‌های محیطی برای بیش از ۵ میلیارد سال است. به بیان دیگر، ما شاهد دو گروه از کهکشان‌های کوتوله در محیط‌هایی کاملا متفاوت با فعالیت‌های ستاره‌زایی کاملا مشابه هستیم. هر دو گروه بیش از ۴ میلیارد سال پیش به ستاره‌زایی خود خاتمه داده‌اند. از سویی دیگر، کهکشان‌های کوتوله‌ای که امروزه در اطراف خوشه‌ها قرار دارند (یعنی مدت زمان بسیار کمی را در معرض محرک‌های محیطی بوده‌اند) اما حضور یک خوشه ستاره‌ای هسته‌ای در آن‌ها تایید شده‌است، در ستاره‌زایی، رفتاری مشابه با کهکشان‌های خاموش تهی‌جاای و رشته‌ای دارند. سوالی که پیش می‌آید این است: در نبود محرک‌های محیطی، چه چیزی سبب از بین رفتن ستاره‌زایی در این کهکشان‌ها می‌شود؟

شکل ۲. نمودار درصد جرم ستاره‌ای تشکیل‌شده در کهکشان‌ها بر حسب زمان. در تصویر فوق، متوسط فعالیت‌ ستاره‌زایی کهکشان‌های کوتوله‌ی خاموش و منزوی (نشان داده شده با خطوط ممتد) را با فعالیت ستاره‌زایی کهکشان‌های کوتوله‌ی خاموش خوشه‌ای مقایسه کرده‌ایم. کهکشان‌های کوتوله‌ای که در مرکز خوشه‌ها قرار دارند با خط‌چین و کهکشان‌های کوتوله‌ای که در خوشه‌ها، میزبان خوشه‌های ستاره‌ای هسته‌ای هستند، با نقطه‌چین مشخص شده‌اند. خطوط بنفش کهکشا‌‌ن‌هایی که ستاره‌زایی سریعی داشته‌اند و خطوط صورتی کهکشان‌هایی که هاله و جمعیت ستاره‌ای خود را در بازه‌ی زمانی طولانی‌تری شکل داده‌اند، نمایش می‌دهد.

خاموشی در حضور سیاهچاله‌ها؟

در سال های اخیر، فعالیت‌ هسته‌های کهکشانی فعال۷ به عنوان یکی از فرآیندهای خاموشی ستاره‌ای در کهکشان‌های کوتوله مورد بحث بوده‌است. فعالیت هسته‌ای کهکشانی فعال به فعالیت‌های شدید و پرانرژی در مرکز برخی از کهکشان‌ها اطلاق می‌شود که معمولا ناشی از حضور یک سیاه‌چاله‌ی پرجرم است. یک سیاه‌چاله با جذب ماده، انرژی زیادی را به صورت تابش در طول موج‌های مختلف تابش می‌کند. این تابش با افزایش دمای گاز میان‌ستاره‌ای و به بیرون راندن بخشی از این گاز، به خاموشی فعالیت ستاره‌زایی در کهکشان‌ منجر می‌شود. بر اساس داده‌های موجود، ما نتوانستیم حضور یا عدم حضور سیاه‌چاله در مرکز این کهکشان‌های کوتوله‌ی خاموش‌ را تایید کنیم. از آن‌جایی که در این بازه‌ی جرمی، معمولا یافتن سیاهچاله‌های مرکزی و تمیزدادن آن‌ها از خوشه‌های ستاره‌ای هسته‌ای کار دشواری است، برای بررسی و مطالعه‌ی این موضوع به داده‌های رصدی بهتری نیاز است.

خودکشی کهکشان‌ها با ستاره‌زایی؟

مطالعات اخیر ثابت کرده‌اند که کهکشان‌ها، فارغ از جرم و محل سکونتشان، دو نوع ستاره‌زایی را در طول زندگی خود تجربه می‌کنند: ستاره‌زایی کوتاه‌مدت و بلندمدت. در شکل ۲، این دوگانگی در فعالیت ستاره‌زایی، حتی در یک نمونه‌ی کوچک کهکشان‌های خاموش‌ تهی‌جاای و رشته‌ای، مشهود است.

کهکشان‌هایی که هاله و جمعیت ستاره‌ای خود را خیلی سریع شکل می‌دهند، فارغ از محیط امروزی‌شان، رفتار ستاره‌زایی مشابهی دارند. این امر در مقایسه‌ی بین کهکشان‌های تهی‌جا و خوشه‌ای در شکل ۲، قابل تشخیص است. این بدان معناست که این کهکشان‌ها در یک بازه‌ی زمانی خیلی کوتاه، بخش بزرگی از جمعیت ستاره‌ای خود را تشکیل داده‌اند. ستاره‌زایی در این بازه‌ی کوتاه، به معنای تشکیل بادهای ستاره‌ای  و فعالیت‌های ابرنواختری۸ شدید است. این فعالیت‌ها می‌توانند با افزایش دمای گاز میان ستاره‌ای و به بیرون راندن بخش زیادی از گاز، سبب خاموش شدن کهکشان‌های کوتوله شوند. البته نقش کلیدی بادهای ستاره‌ای در خاموشی کهکشان‌های کوتوله‌ی کم جرم تا به حال اثبات شده است اما نقش این فرایند برای کهکشان‌های کوتوله‌ی پرجرم، هنوز به درستی درک نشده‌است. ستاره‌زایی شدید، فعالیت‌های ابرنواختری و بادهای ستاره‌ای پس از آن، می‌توانند سبب خاموشی کهکشان‌های کوتوله در تهی‌جاها و حتی در مرکز خوشه‌های کیهانی شوند اما بررسی دقیق‌تر این موضوع، منوط به بررسی داده های دقیق‌تر و مناسب‌تر است.

همچنین کهکشان‌های کوتوله‌ای که هاله و جمعیت ستاره‌ای خود را در بازه‌ی زمانی طولانی‌تری ساخته‌اند، اما میزبان یک خوشه‌ی ستاره‌ای هسته‌ای هستند، فارغ از محیطی که در آن زندگی می کنند رفتار ستاره‌زایی مشابهی را از خود نشان می‌دهند. این امر می‌تواند بدان معنا باشد که شکل‌گیری یا حضور یک خوشه‌ی ستاره‌ای هسته‌ای ممکن است به خاموشی کهکشان‌های کوتوله‌ی میزبان منجر شود. از یک زاویه‌ی دیگر، می‌توان گفت که شکل‌گیری خوشه‌ی ستاره‌ای هسته‌ای، خود نتیجه‌ی یک فرآیند خاموشی (مثل انفجارهای ابرنواختری یا حضور فعالیت‌های هسته‌ای کهکشانی) است و پیدا کردن آن‌ها، مانند یافتن رد پای فرآیندهای خاموشی، به غیر از محرک‌های محیطی، در این کهکشان‌هاست.

آن‌چه که سبب خاموشی کهکشان‌های کوتوله‌ی پرجرم منزوی۹ در تهی‌جاها و رشته‌ها شده‌است، هنوز برای ما مشخص نیست. در این مقاله و با استناد به داده‌ها و نتایجی که به‌دست آوردیم، تنها می‌توانستیم حدس‌هایی را در خصوص فرآیندهای مسئول ارائه دهیم و یافتن پاسخ دقیق‌تر، وابسته به ارزیابی و بررسی داده‌های بهتر است. یافتن این جمعیت بسیار کمیاب از کهکشان‌های کوتوله‌ی خاموش‌ در انزوا بدان معناست که بر خلاف باورهای رایج قبلی، محیط تنها عامل خاموشی کهکشان‌های کوتوله نیست و ما هنوز از یک تصویر واقع‌بینانه از فیزیک باریونی در کهکشان‌ها و فرایند‌های مسئول در خاموشی کهکشان‌های کوتوله بسیار فاصله داریم.

۱. Local group
۲. Quenched
۳. Ram pressure
۴. Voids
۵. Filaments
۶. Nuclear star cluster
۷. Active galactic nuclei
۸. Supernova feedback
۹. Isolated dwarf galaxy

شکل بالای صفحه: کهکشان کوتوله‌ی مسیه ۱۱۰ در فاصله ۲/۷۱ میلیون سال نوری از خورشید. منبع: https://www.starkeeper.it/M110.htm

عنوان اصلی مقاله: The Puzzle of isolated and quenched dwarf galaxies in cosmic voids

نویسندگان: .Bahar Bidaran et al.

لینک اصلی مقاله: https://arxiv.org/pdf/2408.05273

گردآوری: بهار بیداران

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