William Bacon's Homepages/MISSION_MILKY_CENTER



Comments?????
Email the Webmaster!!!!!


Locations of Site Visitors

This page was last updated on November 25,2023


William Bacon's MISSION_MILKY_CENTER Page Index


Status of the Deep Space Network

About the Deep Space Network: Space Communications and Navigation

Information on About the Deep Space Network: Space Communications and Navigation

NASA's Digital Orrery

MAST: Barbara A. Mikulski Archive for Space Telescopes

Map of the Universe from Johns Hopkins University and others.....

Johns Hopkins University (JHU) continues to pad its space community résumé with their interactive map, “The map of the observable Universe”, that takes viewers on a 13.7-billion-year-old tour of the cosmos from the present to the moments after the Big Bang. While JHU is responsible for creating the site, additional contributions were made by NASA, the European Space Agency, the National Science Foundation, and the Sloan Foundation.

JWST's weekly observing schedule:

NASA's Unverse of Learning
An Integrated AstroPhisics STEM Learning and Literacy program

Zooming in on the heart of the Milky Way Captured by ESO

This zoom video sequence starts with a broad view of the Milky Way. We then dive into the dusty central region to take a much closer look. There lurks a 4-million solar mass black hole, surrounded by a swarm of stars orbiting rapidly. We first see the stars in motion, thanks to 26 years of data from ESO's telescopes. We then see an even closer view of one of the stars, known as S2, passing very close to the black hole in May 2018. The final part shows a simulation of the motions of the stars. Credit: ESO/GRAVITY Collaboration


Click here to return to top of page



JWST Telescope Finds a Few Surprises In The Galactic Heart of Milky Way

#milkyway #jwst #astronomy More cool designs are on Amazon: Get a Wonderful Person shirt: Alternatively, PayPal donations can be sent here: Hello and welcome! My name is Anton and in this video, we will talk about new discoveries from the center of the Milky Way galaxy Links: Webb reveals new features in heart of the Milky Way NASA’s Webb Reveals New Features in Heart of Milky Way Release Images from webbtelescope.org Galactic center star formation: Galactic filaments: 0:00 Mysteries of the center of our galaxy 1:10 Galactic center is a super dense region in the middle 2:30 Our telescopes got so good now 2:50 Other regions nearby 3:10 So many supernova remnants and some are extreme 3:50 Galactic filaments 4:10 Sgr B emissions and black hole activity 4:55 Sgr C is least explored, new mysteries found 5:45 Unusual protocluster 6:05 Dark nebula 6:40 Needle like hydrogen filaments #milkyway #jwst #astronomy Support this channel on Patreon to help me make this a full time job: Space Engine is available for free here: Enjoy and please subscribe. Or get a shirt: Twitter: Facebook: Twitch: Bitcoins to spare? Donate them here to help this channel grow! 1GFiTKxWyEjAjZv4vsNtWTUmL53HgXBuvu The hardware used to record these videos: CPU: Video Card: Motherboard: RAM: PSU: Case: Microphone: Mixer: Recording and Editing: Some of the above are affiliate links, meaning I would get a (very small) percentage of the price paid.

Imaging the Galaxy’s Centre in Unprecedented Detail Reveals More Mysterious Filaments

Milky Way centre by the MeerKAT array of 65 radio dishes in South Africa. The image spans 4 times the Moon’s size in the sky. Ian Heywood (Oxford U.), SARAO; Here is a full sized version of the picture that was posted in Astronomy Picture of the Day. Colour processing on the image was done by Juan Carlos Munoz-Mateos (ESO) whose Instagram channel you should definitely check out. Has some of the coolest astro images I’ve seen.

Another version of the MeerKAT image of the Galactic centre Credit: I. Heywood, SARAO

Numerous filaments spanning the Galactic plane. The filaments are identified in the lower panel “Spectral Index” Credit Heywood et al Figure 9

This cirrus cloud-like emission from the Galactic centre super bubble dominates this image. This is traversed by a complex of many parallel filaments. The radio bubble nestles against the diffuse Sagittarius A region in the lower centre of the image. The bright dot near the centre of this region is Sagittarius A*, a 4 million solar mass black hole. This image captures the chaotic complexity of the very heart of our Galaxy. Credit: I. Heywood, SARAO Image Description SARAO

The “hour glass” radio bubbles discovered by MeerKAT extend vertically above and below the plane of the galaxy. Many magnetised filaments can be seen running parallel to the bubbles. (Adapted from results published in Heywood et al. 2019.).

Will Our Black Hole Eat the Milky Way? Putting Supermassive Black Holes in Their Place

As soon as you learn about the supermassive black hole at the center of the Milky Way, your next thought is: is that thing going to destroy our galaxy? In the short term, no, in the long term… maybe? Universetoday's youtube channel Sign up to my weekly email newsletter: Weekly Space Hangout: Astronomy Cast: Support us at:Support us at: Follow us on Tumblr: More stories at ---------------------------------------------------------------------- Follow us on Twitter: @universetoday Like us on Facebook: Instagram - Support us at:Support us at: Instagram - Team: Fraser Cain - @fcain / frasercain@gmail.com /Karla Thompson - @karlaii Chad Weber - Chloe Cain - Instagram: @chloegwen2001 Music: Left Spine Down - “X-Ray” Team: Fraser Cain - @fcain / frasercain@gmail.com Karla Thompson - @karlaii / Karla Thompson's youtube channel Chad Weber - weber.chad@gmail.com Chloe Cain - Instagram: @chloegwen2001 Music: Left Spine Down - “X-Ray”

Catalogue of newly discovered filaments from MeerKAT. Credit Heywood et al Fig 8

A rare, almost-perfect spherical supernova remnant that has been discovered at the edge of the MeerKAT mosaic. Numerous compact radio sources are also visible, many of which signpost supermassive black holes at the centres of galaxies far beyond our own. There is also an intriguing tailed radio source visible on the right of the image, which could be an object in our galaxy moving at high speed, leaving a trailing wake. Credit: I. Heywood, SARAO. Image Description by SARAO

The upper panel’s glowing area shows a synchrotron radiation halo surrounding the supermassive black hole at the centre of the galaxy. The radiation highlights the flows of gas funneling toward the black hole. As the gas approaches the black hole, it is heated beginning to ionize where electrons are stripped from the gas. The ionized gas appears as a “mini-spiral” in the lower panel within about five light years of the central black hole. The scale on the top panel shows 5pc (parsecs or about 16 light years). In other words, this cloud of ionized gases and synchrotron radiation swirling about our black hole is light years across. Credit Heywood et al Figure 14

Karl Jansky’s radio telescope build to rotate on Ford Model-T wheels. This is the first radio telescope ever created. Image courtesy of NRAO CC by 3.0

MeerKAT observatory Credit SARAO


Click here to Jump to Universetoday's associated pages



Click here to return to top of page



Astronomers Scan the Center of the Milky Way for Any Sign of Intelligent Civilizations. Nothing but Silence.

Are there civilizations somewhere else in the Universe? Somewhere else in the Milky Way? That’s one of our overarching questions, and an answer in the affirmative would be profound.

Are there civilizations somewhere else in the Universe? Somewhere else in the Milky Way? That’s one of our overarching questions, and an answer in the affirmative would be profound.

The new MeerKAT image of the Galactic centre region is shown with the Galactic plane running horizontally across the image. Many new and previously-known radio features are evident, including supernova remnants, compact star-forming regions, and the large population of mysterious radio filaments. Colours indicate bright radio emission, while fainter emission is shown in greyscale. Credit: I. Heywood, SARAO. Image description: SARAO

his image shows a portion of the electromagnetic spectrum focusing on radio waves. Image Credit: NASA

A simple schematic of the Milky Way. Image Credit:, By RJHall at English Wikipedia, CC BY-SA 3.0

An artist view of a highly magnetized neutron star. Planets too close to a magnetar would face a magnetic field one trillion times stronger than Earth’s. Magnetars emit extremely powerful xrays and gamma rays which would render life impossible in their vicinity. Credit: Carl Knox/ OzGrav

Zoom into the Center of Our Galaxy

This video sequence zooms into the Hubble Space Telescope view of the galactic core. Hubble's infrared vision pierced the dusty heart of our Milky Way galaxy to reveal more than half a million stars at its core. Except for a few blue, foreground stars, the stars are part of the Milky Way's nuclear star cluster, the most massive and densest stellar cluster in our galaxy. Located 27,000 light-years away, this region is so packed with stars, it is equivalent to having a million suns crammed into the volume of space between us and our closest stellar neighbor, Alpha Centauri, 4.3 light-years away. At the very hub of our galaxy, this star cluster surrounds the Milky Way's central supermassive black hole, which is about 4 million times the mass of our sun.

Betrayed By The Red Edge. How We Can Find Aliens, And Why They Already Know We're Here

People are always worried that alien civilizations will detect the transmissions from our old radio shows and television broadcasts, and send in the invasion fleet. But the reality is that life itself has been broadcasting the existence of life on Earth for 500 million years. Blame it on the plants. In addition to filling the atmosphere with oxygen, plants give off a very specific wavelength visible in infrared radiation. It’s the kind of signal that other civilizations could search for as they’re scanning the galaxy. It’s what we’ll be looking for too. But don’t just blame the plants. Other forms of life have been giving off signals too, signals we can search for as we discover new exoplanets and wonder if they have life there. Information on ESA's ARIEL mission Audio Podcast version: : ITunes RSS: What Fraser's Watching Playlist: Weekly email newsletter: Universetoday's youtube channel Sign up to my weekly email newsletter: Weekly Space Hangout: Astronomy Cast: Support us at:Support us at: Follow us on Tumblr: More stories at ---------------------------------------------------------------------- Follow us on Twitter: @universetoday Like us on Facebook: Instagram - Support us at:Support us at: Instagram - Team: Fraser Cain - @fcain / frasercain@gmail.com /Karla Thompson - @karlaii Chad Weber - Chloe Cain - Instagram: @chloegwen2001 Music: Left Spine Down - “X-Ray” Team: Fraser Cain - @fcain / frasercain@gmail.com Karla Thompson - @karlaii / Karla Thompson's youtube channel Chad Weber - weber.chad@gmail.com References: A search for life on Earth from the Galileo spacecraft from Nature magazine Asteroid-bound spacecraft finds signs of life—on Earth Expanding the Timeline for Earth’s Photosynthetic Red Edge Biosignature (PDF) Exoplanet evolution: Astronomers expand cosmic ‘cheat sheet’ Vegetation’s Red Edge: A Possible Spectroscopic Biosignature of Extraterrestrial Plants (PDF) . GRAVITY Instrument Breaks New Ground in Exoplanet Imaging Cutting-edge VLTI instrument reveals details of a storm-wracked exoplanet using optical interferometry ARIEL SPACE MISSION European Space Agency M4 Mission

ARIEL SPACE MISSION European Space Agency M4 Mission


Click here to Jump to universetoday's associated pages



Click here to return to top of page





This is it! Meet the Supermassive Black Hole at the Heart of the Milky Way

On April 10th, 2019, the international consortium known as the Event Horizon Telescope (EHT) announced the first-ever image of a supermassive black hole (SMBH). The image showed the bright disk surrounding the black hole at the center of the M87 galaxy (aka. Virgo A). In 2021, they followed up on this by acquiring an image of the core region of the Centaurus A galaxy and the radio jet emanating from it. Earlier this month, the European Southern Observatory (ESO) announced that the EHT would be sharing the results from its latest campaign – observations of Sagittarius A*!

Event Horizon Telescope releases first image of Sagittarius A*

May 12, 2022 The Event Horizon Telescope has released the first image of the supermassive black hole Sagittarius A*, which is located in the Milky Way.

The Atacama Large Millimeter/submillimeter Array (ALMA) looking up at the Milky Way and the location of Sagittarius A*, the supermassive black hole at our galactic center. Credit: ESO

What it Takes to Image a Black Hole

May 12, 2022 What does it take to capture an image of the black hole at the centre of our galaxy? This video explains how the Event Horizon Telescope (EHT) works, and how astronomers managed to create one massive Earth-sized telescope big enough to “see” at the edge of black holes.

Size comparison of the two EHT black holes

May 12, 2022 While they may look similar, the two black holes imaged by the Event Horizon Telescope (EHT) Collaboration are actually very different. Sagittarius A* (Sgr A*), the black hole at the centre of the Milky Way, is over a thousand times smaller than the black hole at the centre of the galaxy M87. The reason they appear the same size is because of their relative distances from Earth. This animation demonstrates their massive differences in size by showing what the M87 black hole would look like if it were closer to Earth. The final frame shows the sizes of the two black holes if they were both at the same distance from Earth as Sgr A*.

Meet Sgr A*: Zooming into the black hole at the centre of our galaxy

May 12, 2022 Watch as this video sequence zooms into the black hole (Sgr A*) at the centre of our galaxy. Beginning with a broad view of the Milky Way, we dive into the dense clouds of gas and dust at our galactic centre. The stars here have been observed with ESO’s Very Large Telescope and ESO’s Very Large Telescope Interferometer for decades, the black hole’s immense gravitational pull distorting the orbits of the stars closest to it. Finally, we arrive at Sgr A*, the first image of which has been captured by the EHT collaboration. The black hole is shown by a dark central region called a shadow, surrounded by a ring of luminous gas and dust. The various observations used here were taken at different times, by different teams and with different facilities, and put together for the purpose of the zoom effect. The images go from visible wavelengths at the beginning to infrared, with the very final image being taken at radio wavelengths. Credit: ESO/L. Calçada, N. Risinger (skysurvey.org), DSS, VISTA, VVV Survey/D. Minniti DSS, Nogueras-Lara et al., Schoedel, NACO, GRAVITY Collaboration, EHT Collaboration (Music: Azul Cobalto) This video is available for download (various formats including Ultra HD) on:


Click here to Jump to associated pages from Universetoday



Click here to return to top of page



One Star Flies Past the Milky Way’s Black Hole at 3% the Speed of Light

There’s a population of stars in the heart of our galaxy whipping around Sagittarius A* (the Milky Way’s central supermassive black hole). Astronomers just found the closest, fastest one (so far). It’s called S4716 and it orbits Sag A* once every four years. That makes it officially the fastest star moving at the heart of our galaxy. To give you some perspective, the Sun moves around the center of the galaxy at a much more leisurely pace once every 230 million years.

The K-band (near-infrared) view of the GC observed with NIRC2 (Keck) in 2019.30. This image is high-pass filtered and shows the position of several S stars close to Sgr A*, which is indicated by a black cross. Note that the newly discovered S4716 (lime green elliptical orbit) is the smallest and closest to Sgr A*. Here north is up and east is to the left. Credit: The Astrophysical Journal (2022). DOI: 10.3847/1538-4357/ac752f


Click here to Click here to Jump to Associated pages from universetoday/A>



Click here to return to top of page



Star Formation in the Center of the Milky Way Started at the Core and Then Worked its way out

False-color image of the region Sagittarius B1, as seen by the GALACTICNUCLEUS survey. Credit & ©: F. Nogueras-Lara et al. / MPIA

This is an image of the center of the Milky Way. The bright white area right of center is home to the supermassive black hole Sagittarius A star. Credit: By NASA/JPL-Caltech/ESA/CXC/STScI

The central region of the Milky Way in infrared light, acquired by NASA’s Spitzer Space Telescope. Credit: NASA/JPL-Caltech/S. Stolovy (Spitzer Science Center/Caltech)

The all-sky view that the Gaia survey would have of a simulated Milky-Way-like galaxy. Credit: Sanderson et a


Click here to Click here to Jump to Associated pages from universetoday



Click here to return to top of page



There’s a Blob of Gas Orbiting Around the Milky Way’s Supermassive Black Hole

The Atacama Large Millimeter/submillimeter Array (ALMA) looked at Sagittarius A*, (image of Sag A* by the EHT Collaboration) to study something bright in the region around Sag A*. Credit: ESO/José Francisco Salgado

This shows a still image of the supermassive black hole Sagittarius A*, as seen by the Event Horizon Collaboration (EHT), with an artist’s illustration indicating where the modeling of the ALMA data predicts the superheated blob of gas to be and its orbit around the black hole. Credit: EHT Collaboration, ESO/M. Kornmesser (Acknowledgment: M. Wielgus)


Click here to Click here to Jump to Associated pages from universetoday



Click here to return to top of page



The Milky Way’s Supermassive Black Hole had a Burst of Activity 200 Years Ago. We Just Saw the Echo

Imagery from NASA’s Imaging X-ray Polarimetry Explorer and Chandra X-ray Observatory have been combined to show X-ray data of the area around Sagittarius A*, the supermassive black hole at the core of the Milky Way galaxy. The lower panel combines IXPE data, in orange, with Chandra data in blue. The upper panel depicts a much wider field-of-view of the center of the Milky Way, courtesy of Chandra. The thin white lines layered onto the top panel frame the highlighted area, and indicate that the perspective in the bottom panel has been rotated approximately 45 degrees to the right. The combination of IXPE and Chandra data helped researchers determine that the X-ray light identified in the molecular clouds originated from Sagittarius A* during an outburst approximately 200 years ago. Credits: IXPE: NASA/MSFC/F. Marin et al; Chandra: NASA/CXC/SAO; Image Processing: L.Frattare, J.Major & K.Arcand

A time-lapse movie in infrared light detailing how stars in the central light-year of our Galaxy have moved over a period of 14 years. The yellow mark at the image center represents the location of Sgr A*. Credit: A. Eckart (U. Koeln) & R. Genzel (MPE-Garching), SHARP I, NTT, La Silla Obs., ESO

Illustration of gas cloud G2 approaching Sgr A*. Our central supermassive black hole periodically snacks on clouds and other materials like this. That gives off X-rays and other emissions. (ESO/MPE/M.Schartmann/J.Major)

Milky Way’s Central Black Hole Sonification from NASA's IXPE

Combined images of Sagittarius A*, the supermassive black hole at the center of the Milky Way galaxy, enabled researchers to develop a sonification, or an adaptation of visual information into audible, even musical sounds. In this sonification, adapting data from NASA’s Imaging X-ray Polarimetry Explorer and Chandra X-ray Observatory, an arched line ripples across the image, starting at the lower righthand corner. As it passes over the orange-tinted IXPE data, sounds like digital winds are triggered, particularly where those orange areas are brightest. When the traveling line passes the blue-tinted Chandra data, the resulting notes resemble steel drums. #nasa #shorts #sonification #spacesounds #blackhole

Click here to Click here to Jump to Associated pages from universetoday



Click here to return to top of page





ARTICLES

  • To the PDF section articles

  • To the Flatarticle section articles

  • Pages from Universetoday

    Imaging the Galaxy’s Centre in Unprecedented Detail Reveals More Mysterious Filaments

    James Webb’s First Pictures are Out! But it’s a Work in Progress

    A Galaxy is Making New Stars Faster Than its Black Hole Can Starve Them for Fuel

    Universe today's CATEGORY: ASTRONOMY

    Universe today's CATEGORY: BLACK HOLES

    Universe today's CATEGORY: GALAXIES

    Universe today's CATEGORY: RADIO ASTRONOMY

    Universe today's TAG: GALAXY CENTRE

    Universe today's TAG: MEERKAT

    Universe today's TAG: RADIO ASTRONOMY

    Universe today's TAG: RADIO FILAMENTS

    Universe today's TAG: SAGITTARIUS A*

    Universe today's TAG: SUPERMASSIVE BLACK HOLE


    Click here to return to Imaging the Galaxy’s Centre in Unprecedented Detail Reveals More Mysterious Filaments subsection



    Click here to return to top of page


    Pages from Universetoday.com

    Astronomers Scan the Center of the Milky Way for Any Sign of Intelligent Civilizations. Nothing but Silence.

    Advanced Civilizations Could be Using Dyson Spheres to Collect Energy From Black Holes. Here’s how we Could Detect Them

    Astronomy Jargon 101: Magnetars

    How Badly Will Humanity Freak Out if We Discover Alien Life?

    If Aliens Are Out There, We’ll Meet Them in a Few Hundred Million Years

    Universe today's CATEGORY: ASTRONOMY

    Universe today's CATEGORY: MILKY WAY

    Universe today's CATEGORY: SETI

    Universe today's TAG: CIVILIZATIONS

    Universe today's TAG: GALACTIC CORE

    Universe today's TAG: MILKY WAY

    Universe today's TAG: MURCHISON WIDEFIELD ARRAY

    Universe today's TAG: SEARCH FOR LIFE

    Universe today's TAG: SETI

    Universe today's TAG: TECHNOLOGICAL CIVILIZATIONS


    Click here to return to top of Articles subsection



    Click here to return to top of page



    Click here to return to Astronomers Scan the Center of the Milky Way for Any Sign of Intelligent Civilizations. Nothing but Silence subsection




    This is it! Meet the Supermassive Black Hole at the Heart of the Milky Way

    This is it! On May 12th we’ll see the Event Horizon Telescope’s Image of the Milky Way’s Supermassive Black Hole

    What is Sagittarius A*?

    What are Active Galactic Nuclei?

    M87’s Black Hole is Firing Out Jets that Travel 99% the Speed of Lightx

    This is How a Supermassive Black Hole Feeds

    Einstein. Right again

    Universe Today's CATEGORY: ASTRONOMY

    Universe Today's CATEGORY: ASTROPHOTOS

    Universe Today's CATEGORY: BLACK HOLES


    Click here to Return to the top of this page



    Click here to Return to top of this articles subsection



    Click here to This is it! Meet the Supermassive Black Hole at the Heart of the Milky Way subsection



    One Star Flies Past the Milky Way’s Black Hole at 3% the Speed of Light


    What is Sagittarius A*?

    Milky Way’s Black Hole Sending Out Flares

    Beyond Any Reasonable Doubt: A Supermassive Black Hole Lives in Centre of Our Galaxy

    Universe Today's CATEGORY: ASTRONOMY

    Universe Today's CATEGORY: BLACK HOLES

    Universe Today's CATEGORY: STARS



    Click here to Return to top of this articles subsection





    Click here to Jump to Top of this page





    Click here to Return to One Star Flies Past the Milky Way’s Black Hole at 3% the Speed of Light subsection





    Star Formation in the Center of the Milky Way Started at the Core and Then Worked its way out



    Universe Today's CATEGORY: ASTRONOMY

    Universe Today's CATEGORY: MILKY WAY



    Click here to Return to top of this articles subsection





    Click here to Jump to Top of this page





    Click here to Jump to Return to Star Formation in the Center of the Milky Way Started at the Core and Then Worked its way out subsection





    There’s a Blob of Gas Orbiting Around the Milky Way’s Supermassive Black Hole



    Universe Today's CATEGORY: BLACK HOLES



    Click here to Return to top of this articles subsection





    Click here to Jump to Top of this page





    Click here to Jump to Return to There’s a Blob of Gas Orbiting Around the Milky Way’s Supermassive Black Hole subsection






    The Milky Way’s Supermassive Black Hole had a Burst of Activity 200 Years Ago. We Just Saw the Echo.



    Milky Way’s Black Hole Was Active Recently



    Universe Today's CATEGORY: ASTRONOMY



    Click here to Return to top of this articles subsection





    Click here to Jump to Top of this page





    Click here to Return to the The Milky Way’s Supermassive Black Hole had a Burst of Activity 200 Years Ago. We Just Saw the Echo subsection



    Flat Articles

    eso2208-eht-mw — Science Release Astronomers reveal first image of the black hole at the heart of our galaxy 12 May 2022

    8,000 kilometers per second: Star with the shortest orbital period around black hole discovered

    A first glimpse at the high-productivity star factory in the Galactic Center

    Information on A first glimpse at the high-productivity star factory in the Galactic Center


    Detection of an excess of young stars in the Galactic Centre Sagittarius B1 region

    Information on Detection of an excess of young stars in the Galactic Centre Sagittarius B1 region

    Astronomers detect hot gas bubble swirling around the Milky Way’s supermassive black hole

    Orbital motion near Sagittarius A*
    Constraints from polarimetric ALMA observations

    Detection of an echo emitted by Sagittarius A* 200 years ago from Phys.org



    Milky Way’s Central Black Hole Woke Up 200 Years Ago, NASA’s IXPE Finds

    Information on Milky Way’s Central Black Hole Woke Up 200 Years Ago, NASA’s IXPE Finds



    Click here to return to top of page



    Click here to Retrn to Articles subsection



    PDF ARTICLES

    Statistical Properties of the Population of the Galactic Center Filaments: The Spectral Index and Equipartition Magnetic Field

    Information on Statistical Properties of the Population of the Galactic Center Filaments: The Spectral Index and Equipartition Magnetic Field

    The 1.28 GHz MeerKAT Galactic Center Mosaic

    Information on The 1.28 GHz MeerKAT Galactic Center Mosaic

    X-ray polarization evidence for a 200years-old flare of Sgr A-star

    Information on X-ray polarization evidence for a 200 years-old flare of Sgr A∗ (PDF)


    Click here to return to top of page



    Click here to Retrn to Articles subsection