Portrait_NN1 of_IO a_AT1 Black_JJ Hole_NN1 By_II adapting_VVG a_AT1 global_JJ network_NN1 of_IO telescopes_NN2 ,_, astronomers_NN2 will_VM soon_RR get_VVI their_APPGE first_MD look_NN1 ever_RR at_II the_AT dark_JJ silhouette_NN1 of_IO a_AT1 black_JJ hole_NN1 ._. 
You_PPY have_VH0 probably_RR seen_VVN the_AT TV_NN1 commercial_NN1 in_II which_DDQ a_AT1 cell_NN1 phone_NN1 technician_NN1 travels_VVZ to_II remote_JJ places_NN2 and_CC askes_VVZ on_II his_APPGE phone_NN1 ,_, "_" Can_VM you_PPY hear_VVI me_PPIO1 now_RT ?_? "_" 
Imagine_VV0 this_DD1 technician_NN1 traveling_VVG to_II the_AT center_NN1 of_IO our_APPGE Milky_JJ Way_NN1 galaxy_NN1 ,_, whererin_NN1 lurks_VVZ a_AT1 massive_JJ black_JJ hole_NN1 ,_, Sagittarius_NP1 A_ZZ1 (_( Sgr_NP1 A*_FO )_) ,_, weighing_VVG as_RG much_DA1 as_CSA 4.5_MC million_NNO suns_NN2 ._. 
As_II the_AT technician_NN1 approached_VVN within_II 10_MC million_NNO kilometers_NNU2 of_IO the_AT black_JJ hole_NN1 ,_, we_PPIS2 would_VM hear_VVI his_APPGE cadence_NN1 slow_VV0 down_RP and_CC his_APPGE voice_NN1 deepen_VV0 and_CC fade_VV0 ,_, eventually_RR turning_VVG to_II a_AT1 monotone_NN1 whisper_NN1 with_IW diminishing_JJ reception_NN1 ._. 
If_CS we_PPIS2 were_VBDR to_TO look_VVI ,_, we_PPIS2 would_VM see_VVI his_APPGE image_NN1 turn_NN1 increasingly_RR red_JJ and_CC dim_JJ as_CSA he_PPHS1 became_VVD frozen_VVN in_II time_NNT1 near_II the_AT black_JJ hole_NN1 's_GE boundary_NN1 ,_, known_VVN as_II the_AT ever_RR horizon_NN1 ._. 
The_AT technician_NN1 himself_PPX1 ,_, however_RR ,_, would_VM experience_VVI no_AT slowing_NN1 of_IO time_NNT1 and_CC would_VM see_VVI nothing_PN1 strange_JJ at_II the_AT location_NN1 of_IO the_AT event_NN1 horizon_NN1 ._. 
He_PPHS1 would_VM know_VVI he_PPHS1 had_VHD crossed_VVN the_AT horizon_NN1 only_RR when_CS he_PPHS1 heard_VVD us_PPIO2 say_VVI ,_, "_" No_UH ,_, we_PPIS2 can_VM not_XX hear_VVI you_PPY very_RG well_RR !_! "_" 
He_PPHS1 would_VM have_VHI no_AT way_NN1 of_IO sharing_VVG his_APPGE last_MD impressions_NN2 with_IW us_PPIO2 --_JJ nothing_PN1 ,_, not_XX even_RR light_JJ ,_, can_VM escape_VVI from_II gravity_NN1 's_GE extreme_JJ pull_NN1 inside_II the_AT event_NN1 horizon_NN1 ._. 
A_AT1 minute_NNT1 after_CS he_PPHS1 crossed_VVD the_AT horizon_NN1 ,_, the_AT gravitational_JJ forces_NN2 deep_RR inside_II the_AT hole_NN1 would_VM tear_VVI him_PPHO1 apart_RL ._. 
In_II real_JJ life_NN1 we_PPIS2 can_VM not_XX send_VVI a_AT1 technician_NN1 on_II such_DA a_AT1 journey_NN1 ._. 
But_CCB astronomers_NN2 have_VH0 developed_VVN techniques_NN2 that_CST will_VM soon_RR allow_VVI them_PPHO2 ,_, for_IF the_AT first_MD time_NNT1 ,_, to_TO produce_VVI images_NN2 of_IO a_AT1 black_JJ hole_NN1 's_GE dark_JJ silhouette_NN1 against_II a_AT1 backdrop_NN1 of_IO hot_JJ glowing_JJ gas_NN1 ._. 
Wait_VV0 ,_, you_PPY say_VV0 ._. 
Have_VH0 n't_XX astronomers_NN2 reported_VVN lots_PN of_IO observations_NN2 of_IO black_JJ holes_NN2 ,_, including_II all_DB sorts_NN2 of_IO pictures_NN2 ?_? 
That_DD1 is_VBZ true_JJ ,_, but_CCB the_AT pictures_NN2 have_VH0 been_VBN of_IO gas_NN1 or_CC other_JJ material_NN1 near_II a_AT1 black_JJ hole_NN1 ,_, with_IW the_AT hole_NN1 itself_PPX1 an_AT1 invisible_JJ speck_NN1 ,_, or_CC of_IO huge_JJ outpourings_NN2 of_IO energy_NN1 presumed_VVD to_TO come_VVI from_II a_AT1 black_JJ hole_NN1 ._. 
In_II fact_NN1 ,_, we_PPIS2 do_VD0 not_XX even_RR know_VVI for_RR21 sure_RR22 whether_CSW black_JJ holes_NN2 really_RR exist_VV0 ._. 
&lsqb;_( see_VV0 "_" Black_JJ Stars_NN2 ,_, Not_XX Holes_NN2 ,_, "_" by_II Carlos_NP1 Barcelo_NP1 ,_, Stefano_NP1 Liberati_NP1 ,_, Sebastiano_NP1 Sonego_NP1 and_CC Matt_NP1 Visser_NP1 ;_; SCIENTIFIC_JJ AMERICAN_JJ ,_, October_NPM1 &rsqb;_) ._. 
Astronomers_NN2 have_VH0 detected_VVN objects_NN2 in_II the_AT sky_NN1 that_CST are_VBR sufficiently_RR massive_JJ and_CC compact_NN1 that_CST ,_, if_CS Einstein_NP1 's_GE general_JJ theory_NN1 of_IO relativity_NN1 is_VBZ correct_JJ ,_, they_PPHS2 must_VM be_VBI black_JJ holes_NN2 ,_, and_CC it_PPH1 is_VBZ customary_JJ to_TO talk_VVI of_IO them_PPHO2 as_CS21 if_CS22 they_PPHS2 were_VBDR (_( as_CSA we_PPIS2 do_VD0 in_II this_DD1 article_NN1 )_) ._. 
But_CCB until_II now_RT we_PPIS2 could_VM not_XX tell_VVI if_CS these_DD2 objects_NN2 had_VHD the_AT defining_JJ characteristic_NN1 of_IO a_AT1 black_JJ hole_NN1 --_NN1 a_AT1 horizon_NN1 through_II which_DDQ material_NN1 can_VM flow_VVI only_RR one_MC1 way_NN1 ._. 
This_DD1 question_NN1 is_VBZ not_XX merely_RR a_AT1 matter_NN1 of_IO esoteric_JJ curiosity_NN1 ,_, because_CS such_DA horizons_NN2 are_VBR at_II the_AT heart_NN1 of_IO one_MC1 of_IO the_AT deepest_JJT puzzles_NN2 in_II theoretical_JJ physics_NN1 ._. 
And_CC images_NN2 showing_VVG the_AT dark_JJ silhouettes_NN2 of_IO black_JJ holes_NN2 '_GE event_NN1 horizons_NN2 would_VM help_VVI us_PPIO2 understand_VVI the_AT extraordinary_JJ astrophysical_JJ processes_NN2 taking_VVG place_NN1 in_II their_APPGE neighborhood_NN1 ._. 
Driving_JJ Questions_NN2 Event_NN1 horizons_NN2 are_VBR a_AT1 source_NN1 of_IO fascination_NN1 because_CS they_PPHS2 represent_VV0 a_AT1 fundamental_JJ inconsistency_NN1 between_II two_MC great_JJ triumphs_NN2 of_IO 20th-century_JJ physics_NN1 :_: quantum_NN1 mechanics_NN2 and_CC relativity_NN1 ._. 
Time_NNT1 reversibility_NN1 is_VBZ an_AT1 essential_JJ feature_NN1 of_IO the_AT quantum-mechanical_JJ description_NN1 of_IO physical_JJ systems_NN2 ;_; every_AT1 quantum_NN1 process_NN1 has_VHZ an_AT1 inverse_JJ process_NN1 ,_, which_DDQ may_VM be_VBI used_VVN ,_, in_II principle_NN1 to_TO recover_VVI any_DD information_NN1 that_CST the_AT original_JJ process_NN1 may_VM have_VHI scrambled_VVN ._. 
In_II contrast_NN1 ,_, general_JJ relativity_NN1 --_NN1 which_DDQ explains_VVZ gravity_NN1 as_CSA arising_VVG from_II teh_NN1 curvature_NN1 of_IO space_NN1 and_CC predicts_VVZ the_AT existence_NN1 of_IO black_JJ holes_NN2 --_NN1 admits_VVZ no_AT inverse_JJ process_NN1 to_TO bring_VVI back_RP something_PN1 that_CST has_VHZ fallen_VVN into_II a_AT1 black_JJ hole_NN1 ._. 
The_AT need_NN1 to_TO resolve_VVI this_DD1 inconsistency_NN1 between_II quantum_NN1 mechanics_NN2 and_CC gravitation_NN1 has_VHZ been_VBN one_MC1 of_IO string_NN1 theorists_NN2 '_GE primary_JJ motivations_NN2 in_II their_APPGE quest_NN1 for_IF a_AT1 quantum_NN1 theory_NN1 of_IO gravity_NN1 --_NN1 a_AT1 theory_NN1 that_CST would_VM predict_VVI the_AT properties_NN2 of_IO gravitation_NN1 as_CSA arising_VVG from_II interactions_NN2 following_VVG the_AT laws_NN2 of_IO quantum_NN1 mechanics_NN2 ._. 
On_II a_AT1 more_RGR basic_JJ level_NN1 ,_, physicists_NN2 would_VM like_VVI to_TO know_VVI if_CSW Einstein_NP1 's_GE general_JJ relativity_NN1 really_RR is_VBZ the_AT theory_NN1 of_IO gravity_NN1 ,_, even_RR where_CS it_PPH1 predicts_VVZ shocking_JJ deviations_NN2 from_II classical_JJ ,_, Newtonian_JJ theory_NN1 --_NN1 such_II21 as_II22 the_AT existence_NN1 of_IO event_NN1 horizons_NN2 ._. 
Black_JJ holes_NN2 have_VH0 the_AT twin_NN1 virtues_NN2 of_IO corresponding_VVG to_II extraordinary_JJ simple_JJ solutions_NN2 to_II Einstein_NP1 's_GE equations_NN2 of_IO gravity_NN1 (_( a_AT1 black_JJ hole_NN1 is_VBZ completely_RR characterized_VVN by_II just_RR three_MC numbers_NN2 --_NN1 its_APPGE mass_NN1 ,_, charge_NN1 and_CC spin_NN1 )_) ,_, as_II31 well_II32 as_II33 being_VBG places_NN2 where_RRQ gravity_NN1 differs_VVZ the_AT most_RRT from_II Newtonian_JJ theory_NN1 ._. 
Thus_RR ,_, black_JJ holes_NN2 are_VBR prime_JJ locations_NN2 for_IF seeking_VVG evidence_NN1 of_IO deviations_NN2 from_II Einstein_NP1 's_GE equations_NN2 under_II extreme_JJ conditions_NN2 ,_, which_DDQ could_VM provide_VVI clues_NN2 toward_II a_AT1 quantum_NN1 theory_NN1 of_IO gravity_NN1 ._. 
Conversely_RR ,_, the_AT equations_NN2 '_GE success_NN1 near_II black_JJ holes_NN2 will_VM dramatically_RR extend_VVI the_AT regime_NN1 in_II which_DDQ we_PPIS2 know_VV0 general_JJ relativity_NN1 works_VVZ ._. 
Pressing_JJ astrophysical_JJ questions_NN2 about_II what_DDQ happens_VVZ in_II the_AT vicinity_NN1 of_IO black_JJ holes_NN2 also_RR demand_VV0 answers_NN2 ._. 
Black_JJ holes_NN2 are_VBR fed_VVN by_II infalling_VVG material_NN1 such_II21 as_II22 gas_NN1 and_CC dust_NN1 ._. 
The_AT matter_NN1 gains_VVZ vast_JJ quantities_NN2 of_IO energy_NN1 as_CSA it_PPH1 falls_VVZ closer_RRR to_II the_AT hole_NN1 's_GE horizon_NN1 ,_, producing_VVG heat_NN1 20_MC times_NNT2 more_RRR efficiently_RR than_CSN nuclear_JJ fusion_NN1 ,_, the_AT next_MD most_RGT potent_JJ energy_NN1 generator_NN1 known_VVN ._. 
Radiation_NN1 from_II the_AT hot_JJ ,_, spiraling_VVG gas_NN1 makes_VVZ the_AT environment_NN1 near_II black_JJ holes_NN2 the_AT brightest_JJT objects_NN2 in_II the_AT universe_NN1 ._. 
Astrophysicists_NN2 can_VM model_VVI the_AT accreting_JJ material_NN1 to_II some_DD extent_NN1 ,_, but_CCB it_PPH1 is_VBZ unclear_JJ how_RRQ gas_NN1 in_II the_AT accretion_NN1 flow_NN1 migrates_VVZ from_II an_AT1 orbit_NN1 at_II a_AT1 large_JJ radius_NN1 to_II one_PN1 near_II the_AT horizon_NN1 and_CC how_RRQ ,_, precisely_RR ,_, it_PPH1 finally_RR falls_VVZ into_II the_AT black_JJ hole_NN1 ._. 
Magnetic_JJ fields_NN2 ,_, created_VVN by_II charged_JJ particles_NN2 moving_VVG in_II the_AT accretion_NN1 flow_NN1 ,_, must_VM play_VVI a_AT1 very_RG important_JJ role_NN1 in_II how_RRQ the_AT flow_NN1 behaves_VVZ ._. 
Yet_RR we_PPIS2 know_VV0 little_RR about_II how_RRQ these_DD2 fields_NN2 are_VBR structured_VVN and_CC how_RRQ that_DD1 structure_NN1 affects_VVZ black_JJ hole_NN1 's_VBZ observed_VVN properties_NN2 ._. 
Although_CS computer_NN1 simulations_NN2 of_IO the_AT entire_JJ accreting_JJ region_NN1 are_VBR becoming_VVG feasible_JJ ,_, we_PPIS2 theorists_NN2 remain_VV0 decades_NNT2 away_II21 from_II22 true_JJ ab_JJ21 initio_JJ22 calculations_NN2 ._. 
Input_NN1 from_II observations_NN2 will_VM be_VBI vital_JJ for_IF inspring_VVG new_JJ ideas_NN2 and_CC deciding_VVG among_II competing_JJ models_NN2 ._. 
More_RGR embarrassing_JJ to_II astrophysicists_NN2 is_VBZ our_APPGE lack_NN1 of_IO understanding_NN1 of_IO black_JJ hole_NN1 jets_NN2 --_JJ phenomena_NN2 in_II which_DDQ the_AT forces_NN2 near_II a_AT1 supermassive_JJ black_JJ hole_NN1 somehow_RR conspire_VV0 to_TO spew_VVI out_RP material_NN1 a_AT1 ultrarelativistic_JJ speeds_NN2 (_( up_RG21 to_RG22 99.98_MC percent_NNU of_IO light_JJ speed_NN1 )_) ._. 
These_DD2 amazing_JJ outflows_NN2 traverse_VV0 distances_NN2 larger_JJR than_CSN galaxies_NN2 ,_, yet_RR they_PPHS2 originate_VV0 near_II the_AT black_JJ hole_NN1 as_CSA intense_JJ beams_NN2 collimated_VVD tightly_RR enough_RR that_CST they_PPHS2 could_VM thread_VVI the_AT solar_JJ system_NN1 --_NN1 the_AT eye_NN1 of_IO a_AT1 galactic_JJ needle_NN1 ._. 
We_PPIS2 do_VD0 not_XX know_VVI what_DDQ accelerates_VVZ these_DD2 jets_NN2 to_II such_DA high_JJ speeds_NN2 or_CC even_RR what_DDQ the_AT jets_NN2 are_VBR made_VVN of_IO --_NN1 are_VBR they_PPHS2 electrons_NN2 and_CC protons_NN2 or_CC electrons_NN2 and_CC positrons_NN2 ,_, or_CC are_VBR they_PPHS2 primarily_RR electromagnetic_JJ fields_NN2 ?_? 
To_TO answer_VVI these_DD2 and_CC other_JJ questions_NN2 ,_, astromomers_NN2 desperately_RR need_VM direct_VVI observations_NN2 of_IO the_AT gas_NN1 in_II a_AT1 black_JJ hole_NN1 's_GE vicinity_NN1 ._. 
Stalking_VVG the_AT Behemoth_NN1 from_II Afar_RL Unfortunately_RR ,_, such_DA observations_NN2 are_VBR difficult_JJ for_IF several_DA2 reasons_NN2 ._. 
First_MD ,_, black_JJ holes_NN2 are_VBR extremely_RR small_JJ by_II any_DD astronomical_JJ measure_NN1 ._. 
They_PPHS2 appear_VV0 to_TO come_VVI in_II two_MC main_JJ varieties_NN2 :_: stelar-mass_JJ black_JJ holes_NN2 ,_, the_AT remnants_NN2 of_IO dead_RG massive_JJ stars_NN2 ,_, with_IW typical_JJ masses_NN2 of_IO five_MC to_II 15_MC suns_NN2 ,_, and_CC supermassive_JJ black_JJ holes_NN2 ,_, located_VVN at_II the_AT centers_NN2 of_IO galaxies_NN2 and_CC weighing_VVG millions_NNO2 to_II 10_MC billion_NNO suns_NN2 ._. 
A_AT1 15-solar-mass_JJ black_JJ hole_NN1 's_GE event_NN1 horizon_NN1 would_VM be_VBI a_AT1 mere_JJ 90_MC kilometers_NNU2 in_II diameter_NN1 --_NN1 far_RR too_RG tiny_JJ to_TO be_VBI resolved_VVN at_II interstellar_JJ distances_NN2 ._. 
Even_RR a_AT1 one-billion-sun_JJ monster_NN1 would_VM fit_VVI comfortably_RR inside_II Neptune_NP1 's_GE orbit_NN1 ._. 
Second_MD ,_, a_AT1 black_JJ hole_NN1 's_GE small_JJ size_NN1 and_CC intense_JJ gravity_NN1 make_VV0 for_IF extremely_RR fast_JJ motion_NN1 --_NN1 matter_VV0 very_RG near_II a_AT1 stellar-mass_JJ black_JJ hole_NN1 can_VM compete_VVI an_AT1 orbit_NN1 in_II less_DAR than_CSN a_AT1 microsecond_NN1 ._. 
It_PPH1 takes_VVZ highly_RR sensitive_JJ instruments_NN2 to_TO observe_VVI such_DA rapid_JJ phenomena_NN2 ._. 
Finally_RR ,_, only_RR the_AT small_JJ subset_NN1 of_IO black_JJ holes_NN2 that_CST have_VH0 large_JJ reservoirs_NN2 of_IO nearby_JJ gas_NN1 to_TO accrete_VVI are_VBR visible_JJ at_RR21 all_RR22 ;_; the_AT vast_JJ majority_NN1 of_IO black_JJ holes_NN2 in_II the_AT Milky_JJ Way_NN1 are_VBR ,_, as_RR21 yet_RR22 ,_, undiscovered_JJ ._. 
Rising_VVG to_II these_DD2 challenges_NN2 ,_, astronomers_NN2 have_VH0 developed_VVN a_AT1 variety_NN1 of_IO techniques_NN2 that_CST ,_, short_JJ of_IO providing_VVG direct_JJ images_NN2 ,_, have_VH0 provided_VVN information_NN1 about_II the_AT properties_NN2 and_CC behavior_NN1 of_IO matter_NN1 orbiting_VVG close_RR to_II suspected_JJ black_JJ holes_NN2 ._. 
For_REX21 instance_REX22 ,_, astronomers_NN2 can_VM weigh_VVI a_AT1 supermassive_JJ black_JJ hole_NN1 by_II observing_VVG stars_NN2 near_II it_PPH1 ,_, much_RR like_II using_VVG planets_NN2 '_GE orbits_NN2 to_TO weigh_VVI the_AT sun_NN1 ._. 
In_II distant_JJ galaxies_NN2 ,_, individual_JJ stars_NN2 near_II a_AT1 supermassive_JJ hole_NN1 can_VM not_XX be_VBI resolved_VVN ,_, but_CCB the_AT spectrum_NN1 of_IO their_APPGE light_NN1 indicates_VVZ their_APPGE distribution_NN1 of_IO velocicities_NN2 ,_, which_DDQ yields_VVZ a_AT1 mass_NN1 for_IF the_AT hole_NN1 ._. 
The_AT supermassive_JJ black_JJ hole_NN1 Sgr_NP1 A*_FO at_II the_AT center_NN1 of_IO the_AT Milky_JJ Way_NN1 is_VBZ close_RR enough_RR for_IF telescopes_NN2 to_TO resolve_VVI individual_JJ stars_NN2 near_II it_PPH1 ,_, producing_VVG the_AT best_JJT mass_JJ estimate_NN1 of_IO any_DD black_JJ hole_NN1 to_II date_NN1 &lsqb;_( see_VV0 box_NN1 on_II page_NN1 47_MC &rsqb;_) ._. 
Unfortunately_RR ,_, these_DD2 stars_NN2 are_VBR far_RR outside_II the_AT region_NN1 that_CST interests_VVZ us_PPIO2 most_RRT ,_, where_CS general_JJ relativistic_JJ effects_NN2 become_VV0 significant_JJ ._. 
Information_NN1 about_II how_RGQ much_DA1 spin_NN1 stellarmass_VV0 black_JJ holes_NN2 have_VH0 has_VHZ come_VVN from_II binary_JJ systems_NN2 in_II which_DDQ a_AT1 black_JJ hole_NN1 and_CC an_AT1 ordinary_JJ star_NN1 orbit_VV0 each_PPX221 other_PPX222 close_VV0 enough_RR for_IF the_AT hole_NN1 to_TO slowly_RR feed_VVI on_II its_APPGE companion_NN1 ._. 
Analysis_NN1 of_IO the_AT x-ray_JJ spectra_NN2 and_CC orbital_JJ parameters_NN2 for_IF a_AT1 handful_NN1 of_IO such_DA systems_NN2 indicates_VVZ that_CST the_AT holes_NN2 have_VH0 65_MC to_II 100_MC percent_NNU of_IO the_AT maximum_JJ spin_NN1 permitted_VVN by_II general_JJ relativity_NN1 for_IF a_AT1 hole_NN1 of_IO a_AT1 given_JJ mass_NN1 ;_; very_RG high_JJ spin_NN1 seems_VVZ to_TO be_VBI the_AT norm_NN1 ._. 
Light_NN1 (_( ranging_VVG from_II radio_NN1 waves_NN2 to_II x-rays_NN2 )_) and_CC energetic_JJ jets_NN2 are_VBR not_XX the_AT only_JJ things_NN2 emitted_VVD by_II black_JJ holes_NN2 ._. 
When_CS two_MC black_JJ holes_NN2 collide_VV0 ,_, they_PPHS2 shake_VV0 the_AT fabric_NN1 of_IO spacetime_NNT1 around_II them_PPHO2 ,_, producing_VVG gravitational_JJ waves_NN2 that_CST propagate_VV0 out_RP like_II ripples_NN2 on_II a_AT1 pond_NN1 ._. 
These_DD2 ripples_NN2 of_IO spacetime_NNT1 should_VM be_VBI detectable_JJ at_II vast_JJ distances_NN2 ,_, albeit_CS requiring_VVG incredibly_RR sensitive_JJ instruments_NN2 ._. 
Although_CS observatories_NN2 already_RR operating_NN1 have_VH0 yet_RR to_TO detect_VVI any_DD gravitational_JJ waves_NN2 ,_, the_AT method_NN1 offers_VVZ a_AT1 revolutionary_JJ new_JJ way_NN1 to_TO study_VVI black_JJ holes_NN2 ._. 
&lsqb;_( see_VV0 "_" Ripples_NN2 in_II Spacetime_NNT1 ,_, "_" by_II W._NP1 Wayt_NP1 Gibbs_NP1 ;_; SCIENTIFIC_JJ AMERICAN_JJ ,_, April_NPM1 2002_MC &rsqb;_) ._. 
A_AT1 Window_NN1 with_IW a_AT1 View_NN1 Despite_II providing_VVG a_AT1 wealth_NN1 of_IO information_NN1 ,_, none_PN of_IO the_AT techniques_NN2 we_PPIS2 have_VH0 described_VVN thus_RR far_RR offer_VV0 an_AT1 image_NN1 of_IO a_AT1 black_JJ hole_NN1 's_GE event_NN1 horizon_NN1 ._. 
Now_RT ,_, however_RR ,_, thanks_NN2 to_II very_RG recent_JJ advances_NN2 in_II technology_NN1 ,_, direct_JJ imaging_NN1 of_IO a_AT1 black_JJ hole_NN1 's_GE horizon_NN1 is_VBZ imminent_JJ ._. 
The_AT black_JJ hole_NN1 to_TO be_VBI imaged_VVN is_VBZ the_AT behemoth_NN1 in_II our_APPGE backyard_NN1 ,_, Sgr_NP1 A*_FO ._. 
At_II a_AT1 distance_NN1 of_IO only_RR 24,000_MC light-years_NNT2 ,_, Sgr_NP1 A*_FO occupies_VVZ the_AT largest_JJT disk_NN1 on_II the_AT sky_NN1 of_IO any_DD known_JJ black_JJ hole_NN1 ._. 
A_AT1 10-solar-mass_JJ black_JJ hole_NN1 would_VM have_VHI to_TO be_VBI 1/100th_FU as_RG far_RR away_RL as_CSA the_AT nearest_JJT star_NN1 to_TO appear_VVI as_RG big_JJ ._. 
And_CC although_CS supermassive_JJ black_JJ holes_NN2 much_RR larger_JJR than_CSN Sgr_NP1 A*_FO exist_VV0 ,_, they_PPHS2 are_VBR millions_NNO2 of_IO light-years_NNT2 away_RL ._. 
The_AT dark_JJ silhouette_NN1 of_IO a_AT1 distant_JJ black_JJ hole_NN1 is_VBZ more_DAR than_CSN doubled_VVN in_II apparent_JJ size_NN1 thanks_NN2 to_II the_AT bending_NN1 of_IO light_JJ rays_NN2 by_II the_AT hole_NN1 's_GE gravity_NN1 ._. 
Even_RR21 so_RR22 ,_, Sgr_NP1 A*_FO 's_GE horizon_NN1 will_VM appear_VVI to_TO span_VVI a_AT1 mere_JJ 55_MC microarcseconds_VVZ --_NN1 as_RG small_JJ as_CSA a_AT1 poppy_NN1 seed_NN1 in_II Los_NP1 Angeles_NP1 viewed_VVD from_II New_NP1 York_NP1 City_NN1 ._. 
The_AT resolution_NN1 of_IO all_DB modern_JJ telescopes_NN2 ,_, as_RG impressive_JJ as_CSA they_PPHS2 are_VBR ,_, is_VBZ fundamentally_RR limited_VVN by_II diffraction_NN1 ,_, a_AT1 wave-optics_JJ effect_NN1 that_CST occurs_VVZ as_RG light_JJ passes_NN2 through_II the_AT finite_JJ aperture_NN1 presented_VVN by_II the_AT size_NN1 of_IO the_AT telescope_NN1 ._. 
Generally_RR ,_, the_AT smallest_JJT angular_JJ scale_NN1 resolvable_JJ by_II a_AT1 telescope_NN1 can_VM be_VBI decreased_VVN by_II making_VVG the_AT telescope_NN1 larger_JJR or_CC by_II capturing_VVG shorter_JJR wavelength_NN1 light_NN1 ._. 
At_II infrared_JJ wavelengths_NN2 (_( which_DDQ ,_, conveniently_RR ,_, pass_VV0 through_II dust_NN1 clouds_NN2 that_CST hide_VV0 Sgr_NP1 A*_FO at_II visible_JJ wavelengths_NN2 )_) ,_, an_AT1 angular_JJ scale_NN1 of_IO 55_MC microarcseconds_NN2 would_VM require_VVI a_AT1 telescope_NN1 seven_MC kilometers_NNU2 across_RL ._. 
The_AT shorter_JJR wavelengths_NN2 of_IO visible_JJ or_CC ultraviolet_JJ light_NN1 would_VM somewhat_RR reduce_VVI this_DD1 gargantuan_JJ requirement_NN1 but_CCB not_XX by_II enough_DD to_TO be_VBI any_DD less_DAR ridiculous_JJ ._. 
Considering_CS longer_JJR wavelengths_NN2 might_VM seem_VVI pointless_JJ --_JJ millimenter_NN1 radio_NN1 waves_NN2 ,_, for_REX21 instance_REX22 ,_, would_VM require_VVI a_AT1 telescope_NN1 5,000_MC kilometers_NNU2 across_RL ._. 
But_CCB it_PPH1 just_RR so_RR happens_VVZ that_CST Earthsize_VV0 radio_NN1 telescopes_NN2 are_VBR already_RR operating_VVG ._. 
A_AT1 technique_NN1 called_VVN very_RG long_JJ baseline_NN1 interferometry_NN1 (_( VLBI_NP1 )_) combines_VVZ the_AT signal_NN1 detected_VVN by_II an_AT1 array_NN1 of_IO radio_NN1 telescopes_NN2 sprinkled_VVN around_II the_AT globe_NN1 to_TO achieve_VVI the_AT angular_JJ resolutions_NN2 that_CST an_AT1 Earth-size_JJ radio_NN1 dish_NN1 would_VM achieve_VVI ._. 
Two_MC such_DA arrays_NN2 of_IO telescopes_NN2 have_VH0 been_VBN operating_VVG for_IF more_DAR than_CSN a_AT1 decade_NNT1 --_NN1 the_AT Very_RG Long_JJ Baseline_NN1 Array_NN1 (_( VLBA_NP1 )_) ,_, with_IW dishes_NN2 in_II the_AT U.S._NP1 as_RG far_RR afield_RL as_CSA Hawaii_NP1 and_CC New_NP1 Hampshire_NP1 ,_, and_CC the_AT European_JJ VIBI_JJ Network_NN1 (_( EVN_NP1 )_) ,_, with_IW dishes_NN2 in_II China_NP1 ,_, South_NP1 Africa_NP1 and_CC Puerto_NP1 Rico_NP1 ,_, as_II31 well_II32 as_II33 Europe_NP1 ._. 
You_PPY may_VM remeber_NN1 seeing_VVG a_AT1 much_RR smaller_JJR system_NN1 ,_, the_AT Very_RG Large_JJ Array_NN1 in_II New_NP1 Mexico_NP1 ,_, in_II movies_NN2 such_II21 as_II22 Contact_NN1 and_CC 2010_MC ._. 
