▁the ▁distance ▁by ▁obser ving ▁C ep heid ▁variable ▁stars ▁within ▁I ▁Z wick y ▁ 1 8 . ▁ ▁These ▁massive ▁flash ing ▁stars ▁pul se ▁in ▁a ▁regular ▁rh ythm . ▁The ▁timing ▁of ▁their ▁p uls ations ▁is ▁directly ▁related ▁to ▁their ▁bright ness . ▁The ▁team ▁determined ▁the ▁observed ▁bright ness ▁of ▁three ▁C ep he ids ▁and ▁compared ▁it ▁with ▁the ▁actual ▁bright ness ▁predicted ▁by ▁theoretical ▁models . ▁These ▁models ▁were ▁calculated ▁specifically ▁for ▁I ▁Z wick y ▁ 1 8 ' s ▁def ic iency ▁in ▁heavy ▁elements , ▁indicating ▁the ▁galax y ' s ▁stars ▁formed ▁before ▁these ▁elements ▁were ▁abund ant ▁in ▁the ▁universe . ▁The ▁C ep heid ▁distance ▁also ▁was ▁valid ated ▁through ▁the ▁observed ▁bright ness ▁of ▁the ▁bright est ▁red ▁stars ▁older ▁than ▁one ▁billion ▁years . ▁ ▁The ▁Hub ble ▁data ▁suggest ▁that ▁I ▁Z wick y ▁ 1 8 ▁is ▁ 5 9 ▁million ▁light - year s ▁from ▁Earth . ▁The ▁galax y ' s ▁larger - than - expected ▁distance ▁may ▁explain ▁why ▁astronom ers ▁have ▁had ▁difficulty ▁detect ing ▁older , ▁f ain ter ▁stars ▁within ▁the ▁galax y . ▁The ▁faint , ▁old ▁stars ▁in ▁I ▁Z wick y ▁ 1 8 ▁are ▁almost ▁at ▁the ▁limit ▁of ▁Hub ble ' s ▁resolution ▁and ▁sens itivity . ▁ ▁Classification ▁I ▁Z wick y ▁ 1 8 ▁is ▁class ified ▁as ▁a ▁d war f ▁irregular ▁galax y ▁and ▁also ▁a ▁blue ▁compact ▁galax y